I would suggest that the first community split into denominations rather quickly. There were tensions in the Jerusalem community, such as the feeding and care of widows in Acts, chapter 6. Then in chapter 10, the vision of Peter indicates that the question of whether one had to be a Jew first was one of the early questions that would create other denominations, such as the Ebionites. Peter is then challenged by the Judiazers, to borrow a term from Paul in chapter 11. And then in chapter 15, we find two sets of doctrine agreed upon. The differences are greater than those of most modern denominations. All this is against and extra-Biblical context of Gnosticism, Marcionism, and many other groups that also would have considered themselves Christian. And the believers in John the Baptizer were around, as witnessed by the report on Apollos, who only knew the baptism of John. In fact, in the 19th century Catholic missionaries to Mesopotamia found them still active. I forget the name they go by now, but an article I read last year indicates that there are still around 40,000 in the world.