The Muratorian Canon, which is usually dated to around 170 (before Irenaeus),* provides a list of canonical books that were accepted by the church at Rome at the time of writing.
In one place, it makes the following claim:
“the blessed Apostle Paul himself, imitating the example of his predecessor, John, wrote to seven churches only by name” (lines 47–50).
Since Paul finished writing to the seven churches by around 62 at the latest, if not earlier, the Muratorian Canon must have placed Revelation in the reign of either Nero or Claudius.
The unusual nature of this claim has been noted by a number of scholars. Barclay, for examples, refers to it as an “astonishing statement” (Barclay, Introduction to John, 32).
With a few exceptions (see below), there does not seem to be much dispute within scholarship regarding the fact that it places John’s writing of Revelation prior to Paul’s writing of his letters.
According to Michael J. Kruger, however, the MC only claims that John “legitimizes Paul’s written corpus to seven churches by writing to seven churches of his own.”
Clearly this does not do justice to the claim that Paul was following the example already laid down by his predecessor.
Mark Hitchcock, whose dissertation on the dating of Revelation argued that the early Christians overwhelmingly placed Revelation late in Domitian’s reign focused on the claim that John was Paul’s predecessor and likewise did not address the MC‘s claim that Paul was following his example when he wrote to seven churches.
In seeking to refute Gentry‘s use of it for the early date, Hitchcock points out inconsistencies between what the MC says and Gentry’s own position on dating (since, he argues, it would mean Revelation was written no later than 62 whereas Gentry places it in 64 or later). However, Hitchcock does not seem to concede that it provides evidence for an early and non-Domitianic dating, thus challenging his thesis that the early church almost unanimously held to the late date.
Gentry asserts that this means that John wrote to the seven churches in Asia before Paul. He says that this manuscript “virtually demands the early date for Revelation.”A Defense of the Domitianic Date of the Book of Revelation, p. 52.
But Gentry simply asserts what the MC actually clearly seems to say.
Hitchcock (drawing from the nineteenth-century scholar William Milligan’s commentary on Revelation ), does not address the fact that Paul was said to have followed John’s example by writing to seven churches. Clearly, if a person follows another person’s example, then the other person was first to do it.
The Muratorian Canon’s claim is unambiguous and must be admitted, no matter how strange it might be. Thus, we must conclude that the Domitianic dating of Revelation was not the only narrative known to the early church.
* I would hold that it follows Hippolytan sources written around the year 200, but that it might have been written some decades later.
Further reading: John’s Claudian (41-54) Exile
 Michael J. Kruger, “The Reception of the Book of Revelation in the Early Church,” in Book of Seven Seals: The Peculiarity of Revelation, its Manuscripts, Attestation and Transmission, ed. Thomas J. Kraus and Michael Sommer (WUNT 363; Tübingen: Mohr Siebeck, 2016), 164.
 William Milligan, The Revelation of St. John (London: Macmillan, 1886), 309.