Most commentators, ancient and modern, think that the Book of Revelation received its present form in the last years of the reign of Domitian (81–96). Internal evidence can be adduced that confirms this external consensus.
I'm going to take a minute and explain that God can change anything that does not involve a contradiction or that does not go against His unchangeable nature ( Mal. 3:6 ; 2 Tim. 2:13 ; Titus 1:2 ; Heb. 6:18 ). God can change non-moral things without any apparent or stated reason. Sometimes God commands change because of the changing conditions of humanity.
A major reason for change is that God has an unfolding plan. This plan has stages in which some things are necessary and stages where something else is necessary. Once a prophecy “type” has been fulfilled (the blood of the lamb), when the reality comes, the type is no longer needed. Once the foundation of the church was laid in the apostles ( Eph. 2:20 ), the apostles were no longer needed.
Also, people wander from God and invent fabrications as occurred in pagan antiquity and occur today with the advent of Islam and other false religious systems and cults. Sometimes people repent and want reform. If they are unsuccessful within the existing context, then they create a new one. The Protestant reform and the Catholic counter reform provide examples but there are many. Humanity's freewill predicates change.
But back to God. In view of the principle of progressive revelation, the later revelations are not contradictory, but complementary. They do not make mistakes, but reveal more truth. Later revelations do not negate the former; they simply replace them. Since they were not given for all, but only for a specified time, they do not conflict when they change. No two opposing commands are for the same people at the same time.
God does not reveal everything at once, nor does he lay down the same conditions for every period of history. Some of his later revelations will supersede his earlier statements. Bible critics sometimes confuse a change in revelation with a mistake. It's not. It's progressive revelation.
The point here is that God's unfolding plan and prophecy in a sin permeated world housing a willful humanity residing in an angelic conflict is reason enough to begin to question the preterist (which atheists prefer) view that John intended everything he wrote in Revelations to occur in his lifetime.
And once you begin that study, it becomes apparent that it is so. An example, the final manifestation of the beast and false prophet (when tied to Paul's Man of Sin) seems to indicate that John's series of antichrists (whether John here envisions this or not) will indeed give way to a final end-times persecutor of the people of God, in which the state uses its powers to impose the false teaching described by John on the people of God.
In fact, both John (Rev. 20:1-10) and Paul (2 Thess. 2:1-12) speak of Satan's power as currently restrained, in some way, until the time of the end... an end in which travel and knowledge have dramatically increased far past John's time. And this may be why John here speaks of a series of antichrists and not an Antichrist (indeed, John believes many antichrists have already come).
I could go on and on but I have things to do. Peace.
I think the author of Revelation was referring to Roman society of the day. It was not his intention to address Christians 2000 years into the future.