We will see once more that the question is much more complex.
1. Generic epithets for Τροίη / Ἴλιος
in the accusative in
and in the genitive in
or at a different place in the verse, as for other places like Calydon and Gonoessa:
ὃς πάσῃ Πλευρῶνι καὶ αἰπεινῇ Καλυδῶνι (13.217; cf. 14.116)
This epithet never appears with the name Τροίη, but no holder of the realist theory like Bowra would say that Ἴλιος was lofty and Τροίη was not.
ὑψίπυλος ‘with high gates’
Τροίῃ ἐν εὐρείῃ, τῶν δ᾽ οὔ τινά φημι λελεῖφθαι (Iliad 24.256 = 494; cf. Odyssey 1.62, 4.99, 5.307)
Line-final ἐνὶ Τροίῃ εὐρείῃ is built on the same fundamental schema as ἐν Λυκίῃ εὐρείῃ (Iliad 6.210), Λυκίης εὐρείης (Iliad 6.173), ἐν Κρήτῃ εὐρείῃ (Odyssey 13.256, etc.), and (with an even closer resemblance) ἐνὶ Σπάρτῃ εὐρείῃ (Odyssey 11.460) and ἐνὶ Κνωσῷ εὐρείῃ (Odyssey 18.591), all at line-end. With Λυκίη another schema is possible, exemplified by:
We observe here a “grammar of the formula,”  with three main possibilities, corresponding to spondaic place-names like Κρήτη and Τροίη, or with short vowels like Λυκίη:
- at verse beginning: ἐν εὐρείῃ – –
- at verse end: ἐνὶ / ἐν – – εὐρείῃ·
- Names with the shape ⏑ ⏑ – , like Λυκίη, can be situated at various positions in the verse, including in line-final formulas.
we find interesting examples of the (locative) dative with preposition ἐν / ἐνὶ in a central position, for example:
φθίσειν ἐν Τροίῃ ἐριβώλακι τηλόθι πάτρης (Iliad 16.461; cf. 24.86)
τῆλ᾽ ἀπὸ Λαρίσης ἐριβώλακος, οὐδὲ τοκεῦσι (Iliad 17.301; cf. 2.841)
Βώρου, ὃς ἐκ Τάρνης ἐριβώλακος εἰληλούθει (Iliad 5.44)
ὅι ῥ᾽ ἐξ Ἀσκανίης ἐριβώλακος ἦλθον ἀμοιβοὶ (Iliad 13.793)
τῶν ὅσσοι Λυκίην ἐριβώλακα ναιετάουσι (Iliad 16.172)
ὅς ῥ᾽ ἐκ Παιονίης ἐριβώλακος εἰληλούθει (Iliad 17.350)
῾Ρίγμον, ὃς ἐκ Θρῄκης ἐριβώλακος εἰληλούθει (Iliad 20.485; cf. 11.222)
κεῖθ᾽ ἁλὶ κεκλιμένη ἐριβώλακος ἠπείροιο (Odyssey 13.325)
We may note that, while the epithet occurs in the genitive case with many toponyms (Λαρίσης, Τάρνης, Ἀσκανίης, Παιονίης, Θρῄκης) and with the common noun ἠπείροιο, there are no occurrences with the genitive Τροίης.
εὐρυάγυια ‘with wide streets’
οὐ γὰρ ἔτι Τροίην αἱρήσομεν εὐρυάγυιαν (Iliad 2.141= 9.28)
τῷ δεκάτῳ δὲ πόλιν αἱρήσομεν εὐρυάγυιαν (Iliad 2.329) 
ἠὲ διεπράθετο πτόλις ἀνδρῶν εὐρυάγυια (Odyssey 15.384)
σῇ δ᾽ ἥλω βουλῇ Πριάμου πόλις εὐρυάγυια (Odyssey 22.230)
The epithet also occurs once with Μυκήνη at the end of the verse:
Even though this is its only attestation within the Homeric corpus, εὐρυάγυια Μυκήνη should very likely be counted as a formula.
2. εὐτείχεος ‘with strong walls’: generic or specific?
We also find two instances with Τροίην εὐτείχεον:
ἱέμενος Τροίην εὐτείχεον ἐξαλαπάξαι (Iliad 8.241)
We may also note the alternative form εὐτειχής without either of the proper names, but with a clear reference to Troy through the word πόλιν in
Τροίην εὔπυργον has a different metrical shape from the more usual Τροίην εὐτείχεον, necessitating a different placement in the verse, but both phrases exhibit a similar distribution around the caesura (penthemimeral or hepthemimeral). Thus Τροίην εὔπυργον may reasonably be considered a formula, entering the complex system of the formulaic epithets for Troy.
Here, however, the adjective αἰπύς, modifying ὄλεθρος, could substitute for αἰπεινή (attested with Ἴλιος, not with Τροίη; see above) or αἰπύς, which also occurs once with Ἴλιος:
Ἴλιον αἰπὺ ἕλοιεν Ἀθηναίης διὰ βουλὰς (Iliad 15.70-71)
Note also the lines
Ἴλιος αἰπεινὴ· νῦν τοι σῶς αἰπὺς ὄλεθρος (Iliad 13.772-773)
in which the formula Ἴλιος αἰπεινὴ at the beginning of the verse occurs in close proximity with the final formula αἰπὺς ὄλεθρος. We may consider this an indication of the relation between the elevation of the city and the abruptness of its destiny in the poet’s mind. Thus the abruptness of the city becomes a metaphor of its destiny, and the metaphor is achieved in the traditional formulaic style. In 17.153 (quoted above) the application of the epithet to ὄλεθρος alone, with the dramatic dative Τροίῃ standing alone at the beginning of the same verse, could thus emphasize the metaphorical value of the epithet, the high city becoming the victim of a high fall, as if there were a fitting proportion between its high walls and the fall. It is of course possible that we attach too much importance to the usual way an epithet occurs and to the contrast with the occurrence where it is missing: we just want to point out a possible stylistic and rhetorical device. 
Note that this is particularly the case for locative expressions: this could lead to support for Sale’s observation that there are no formulas for the locative meaning “in Troy” and for departing from it, and for his hypothesis: the dramatization of the plot inside the city would correspond to the poet’s period, when no more formulas were created anew;  we will come back to this issue.
3. Possible specific epithets and the Holy City
All of the other Iliadic instances reverse the order of name and epithet, as in
Παρνησοῦ, τάχα δ᾽ ἵκανον πτύχας ἠνεμόεσσας (Odyssey 19.432)
As in the Iliad, the epithet occupies the last position in the verse, but the association with ἄκριας or πτύχας instead of Ἴλιος seems to indicate a disregard of the traditional formulaic system.
εὔπωλος ‘abounding in horses’
Thus εὔπωλος could be a specific epithet for this city, known in mythology for the divine horses given by Zeus to Tros as compensation for the taking of his son Ganymede (Iliad 5.266). That is not to say that other places were not also known for their horses, such as Argos, for which the epics use other formulas, especially employing the epithet ἱππόβοτος (the word probably characterizes Argos as a large country rather than a city, as may be the case for Ἴλιος when it is said to be εὔπωλος). 
Τρωσὶν ἐφ᾽ ἱπποδάμοισιν (Iliad 4.355, 19.237, 318)
Τρῶας ἐς ἱπποδάμους (Iliad 17.230)
Τρῶας θ᾽ ἱπποδάμους καὶ ἐϋκνήμιδας Ἀχαιούς (Iliad 3.343, 4.80)
Τρώων ἱπποδάμων (Iliad 2.230, 4.355, 6.461, 11.568)
Τρώων θ’ ἱπποδάμων καὶ Ἀχαιῶν (χαλκοχιτώνων) (Iliad 3.127, 3.131, 4.352, 8.71)
In the whole-verse formulas Τρώων θ’ ἱπποδάμων καὶ Ἀχαιῶν χαλκοχιτώνων and Τρῶας θ᾽ ἱπποδάμους καὶ ἐϋκνήμιδας Ἀχαιούς, clustered in Books 3 and 4, and each denoting the same two groups, note that, although the first hemistich is identical, the second shows a change of both word-order and epithet.
The other formulas quoted above may also, with slight variations, be encountered at other places in the verse, as in
πῶς γὰρ νῦν Τρώεσσι μεμιγμένοι ἱπποδάμοισιν (Iliad 10.424; cf. 17.418, 20.180)
The epithet also occurs with the names of several individuals, including Hector and Antenor among the Trojans, and Tydeus, Diomedes, Nestor, Thrasymedes, and Atreus among the Achaeans (all fighters in the Trojan War or their ancestors), but with no other collective name. So it can be concluded that it is a specific epithet for the Trojans, as εὔπωλος is with Ἴλιος, showing once more the complementarity between Ἴλιος and Τροίη.
ὀφρυοέσσα ‘with overhanging brows’
Ἴλιος ὀφρυόεσσα πυρὶ σμύχοιτο κατ᾽ ἄκρης (Iliad 22.410-411)
The phrase Ἴλιος ὀφρυόεσσα at the beginning of the verse looks like a formula, and though we find no other instance of it, we would be less confident than most “hard Parryist” scholars about excluding its formulaic status:  in a tradition that can be traced back to Meillet,  we admit the possibility of formulas that occur only once in the Homeric corpus. Nevertheless, the opacity of the epithet, already problematic in antiquity for the scholiast quoted by Bowra (above), leads us to conclude that this epithet may be very ancient, and not at all an invention of “Homer,” whatever its meaning is. The formal relation of ὀφρυόεσσα to ὀφρῦς is clear, but does it mean ‘eyebrow’ with an anthropomorphic meaning? Or is the meaning of ‘eyebrow’ for the substantive itself derived from another meaning, which could be attributed to natural features as well as to eyebrows (as seems to be the case in English for brow)?  It happens elsewhere that semantically opaque expressions that can be illuminated by comparison with other languages and/or literatures appear in Homer, Hesiod, Pindar, etc., as very ancient formulas that were obviously not very well understood. Could ὀφρυόεσσα, then, be the sole attested instance of an old epithet specific to Ἴλιος? Ιf we take into account the masculine form ὀφρυόεντα found in an oracle for Corinth preserved by Herodotus,  the epithet would be specific for this city situated on a steeper rock than Troy. It is impossible to go further with such evidence. But it might be important that this passage with a very specific epithet deals in a very solemn tone with the tragic loss of the city, as was the case above with the “high disaster” (αἰπὺς ὄλεθρος) coming to the high city with its high walls. It might also be important to mention that Ophryneion is a toponym known in the Troad, at least through Strabo, who situates a grove sacred to Hector there (13.1.29):  our hypothesis would be that this name derives from the same ὀφρῦς as the epithet ὀφρυόεσσα, based on a similar meaning of ὀφρυ-, let us say ‘brow’ or ‘ravine’, itself relatively frequent in geographical descriptions.
ἱερή / ἱρή ‘sacred’
Especially worthy of note is the line
Although, as we will see shortly, Πέργαμος is the name of the Trojan acropolis, ἱερὴ is a generic epithet in reference to the city of the Trojans.
occurs twice in the Iliad. There are other instances of the phrase in the nominative case:
as well as in the genitive:
The epithet is most frequent in the accusative case. We observed two recurring whole line formulas, and in these instances its formularity is evident:
βῆ δὲ κατ᾽ Ἰδαίων ὀρέων εἰς Ἴλιον ἱρήν (Iliad 15.169; cf. Iliad 24.143, Odyssey 11.86, 17.293)
There are, as well, a number of instances of the verse-final formula Ἴλιον ἱρήν in other contexts (Iliad 5.648, 6.416, 18.270, 21.515, 24.383).
εἴ κεν Ἀχαιοὶ / Τρῷας δῃώσωσιν ἕλωσί τε Ἴλιον ἱρήν (Iliad 4.415-416)
εἰ γᾶρ νῦν Τρώεσσι μένος πολυθαρσὲς ἐνείη / … αἶψά κε Πάτροκλον ἐρυσαίμεθα Ἴλιον εἴσω (Iliad 17.156-159) 
Sale aptly remarks that typical formulas exist for expressing a move towards the city (compare the examples of προτὶ Ἴλιον ἠνεμόεσσαν and προτὶ / εἰς Ἴλιον ἱρὴν, noted above),  whereas there are virtually no formulas corresponding to the locative meaning of ‘in the city’, nor to the expression of the movement away from the city. Sale explains this by a hypothesis concerning the relative chronology of the text, the Troy-scenes that imply the locative being composed, in his opinion, more or less at the date of “Homer.” This conclusion might be in harmony with that of the importance of the space between the Achaean ships and the city walls as the theater of war, which we are exploring.
4. The names of Troy
Αἰνείαν δ’ ἀπάτερθεν ὁμίλου θῆκεν Ἀπόλλων / Περγάμῳ εἰν ἱερῇ (Iliad 5.445-446)
ὣς εἰπὼν αὐτὸς μὲν ἐφέζετο Περγάμῳ ἄκρῃ (Iliad 5.460, with reference to Ares; cf. 6.512-613)
Πέργαμον εἰσαναβᾶσα φίλον πατέρ’ εἰσενόησεν (Iliad 24.700, with reference to Cassandra)
While Pergamos appears to be the proper name of Troy’s acropolis, ἐν πόλει ἄκρῃ can be considered a “minimal formula” for this part of the city.  Pergamos was probably the solemn, official name contrasting with the quotidian use of ἐν πόλει ἄκρῃ.
5. The Names of Troy and Formulaic Economy
Τροίην ἐρίβωλον ἱκέσθην [P 6-12] 1x
ναίοιτε Τροίην ἐριβώλακα [P 1-8] 1x
ναίοιμεν Τροίην ἐριβώλακα [P 1-8] 1x
ἐνὶ Τροίῃ ἐριβώλακι [P 2b-8] 1x
ἐν Τροίῃ ἐριβώλακι [P 3-8] 2x
Τροίην αἱρήσομεν εὐρυάγυιαν [P 4-12] 2x
πόλιν εὐρυάγυιαν [P 7½-12] 5x 
῎Ιλιος αἰπεινή [P 1-5] 1x
῎Ιλιον αἰπεινὴν [P 1-5] 2x
᾽Ιλίου αἰπεινῆς [P 1-5] 3x 
ὑψίπυλον Τροίην [P 3-7] 2x
With the idea ‘broad’ appears a subsystem in the dative:
Τροίῃ ἐν εὐρείῃ [P 1-5] 5x
Another interesting subsystem appears with εὐτείχεος, which occurs with both names in different metrical patterns:
Τροίην εὐτείχεον [P 4-8b] 2x 
Possible specific epithets:
ὑπὸ Ἴλιον ἠνεμόεσσαν [P 6a-12] 1x
Ἴλιον εἰς εὔπωλον [P 1-6a] 2x
ἱππόδαμοι Τρῶες [P 3-7] 2x
Τρώων (θ᾽) ἱπποδάμων [P 1-5] 9x
Τρωσὶν ἐφ᾽ ἱπποδάμοισι(ν) [P 1-6] 4x 
Τρῶάς θ᾽ ἱπποδάμους [P 1-5] 3x
Ἴλιος ὀφρυόεσσα [P 1-6a] 1x
ἱερή and ἱρή
Ἰλίου ἱρῆς [P 9-12] 3x
Ἴλιον εἰς ἱερήν [P 1-5] 1x
Τροίης ἱερὰ κρήδεμνα [P 4-10a] 1x
Τροίης ἱερὸν πτολίεθρον [P 6a-10a] 1x in the Odyssey
Περγάμῳ εἰν ἱερῇ [P 1-5] 1x
Most of these epithets indicate that Ἴλιος and Τροίη refer to different realities, maybe because they have different founders. Or possibly the poets used different metrical shapes, associated with different epithets, to single out different periods in the city’s stratified history. We cannot explain why only Ἴλιος occurs in the nominative, but it might have to do with the fact that, in several cases, the formulas relative to this name are declined (῎Ιλιος αἰπεινή and ῎Ιλιος ἱρή) whereas those with Τροίη are not, and with the fact that Ἴλιος and its paradigm often appear at the beginning of the verse, in an apparently emphatic position. Thus the formulaic system clearly functions according to Parry’s characterization:
The numerous epithets that occur with both Ἴλιος and Τροίη (ἐρίβωλος, ἐριβῶλαξ, εὐρυάγυια, etc.) exhibit a variety of metrical shapes, providing considerable flexibility when joined with either name.
Sale then takes a further step (ibid.):
Sale does not analyze the formulaic system of the names for Troy, because he is interested in what he calls the formularity of place-names (more generally than Troy) in the Iliad, which means the statistical proportion of formulas vs. non-formulaic uses of words. He concludes that ‘in Troy’ does not occur in formulas, but he introduces a note of caution with the qualifiers ‘often’ and ‘frequently’. It is true that the uses of ἐν(ὶ) Τροίη with both ἐριβώλακι and εὐρείῃ are formulaic and are used to express that some event happened ‘in Troy’. Nethertheless, in my opinion, these uses do not imply that Sale’s intuition is wrong: they do not belong to the real Trojan scenes he had in mind, for instance the scenes on the wall in Books 6 and 22, in Priam’s palace, etc. Rather, they all refer to the period before the war, when the “best man who was in Troy married Hippodameia” (Iliad 13.433), when Priam’s sons were born, or when Hector was still protecting his family (three examples in Book 24), and further in the Odyssean examples. They all belong to a timespan before the period narrated in the Iliad, and they derive from that a nostalgic tone. The poet never uses those phrases when he tells for instance of Helen inside the palace or on the walls, of Hector’s quest for Andromache and their meeting, or of the sacrifice scene to Athena. Actually, Sale does not notice some formulaic uses meaning ‘in Troy’, but this does not compromise his conclusions.
Thus “P 6-12,” for example, indicates that the first syllable of the phrase falls in Sicking’s Position 6 and the last syllable in Position 12 (which is the last syllable of the verse). The “masculine” (penthemimeral), “feminine,” and hepthemimeral caesurae fall at the boundaries between positions 5 / 6a, 6a / 6b, and 7 / 8a, respectively.