By the time John received this vision, Paul had been martyred thirty years, and his letters were well-known to all the churches and received as authoritative everywhere.
If Paul was martyred in the early part of AD 60s as the Britannica suggests (and most church historians agree), and John was exiled to Patmos in AD 95 or 96 where he saw the vision, then Paul had been martyred at least 30 years.
“So the curtain falls for the last time. But Paul’s fate is hardly obscure. He himself saw that the charge against him, unrebutted by independent evidence, must bring him to the executioner’s sword, the last penalty for a Roman citizen. … But the traditional date (June 29) reaches us only on far later authority. Acts simply suggests the first half of A.D. 62; and we may imagine Timothy reaching Rome in time to share Paul’s last days (cf. Heb. xiii. 23).”
“Paul, The Apostle,” The Encyclopaedia Britannica, Vol. 20, p. 952.
“The four Gospels and Paul’s epistles—indeed the bulk of the New Testament—were regarded as authoritative from the first.”
LeRoy Froom, The Prophetic Faith of Our Fathers, Vol. 1, p. 101.
Note: Froom includes a helpful timeline chart dated with the concurrent secular history of the Roman Empire and the Caesars, alongside the activity of the first-century church and the dates of writing and authorship of each of the books of the New Testament:
“For the allocation of books in the accompanying chart, the works of fifty of the most learned of the conservative scholars have been consulted and the preponderant evidence tabulated on disputed points as to dating—such as that of James, Galatians, the Synoptics, Jude, and Peter. Absolute certainty cannot be claimed, but the key books are securely anchored, and the essential outline may be considered dependable.”
LeRoy Froom, The Prophetic Faith of Our Fathers, Vol. 1, pp. 97-100.