What communities did the early Christian documents come from?

1 Corinthians 15 often comes up in the context of Easter. A lot of attention is given to the state of the Corinthian church at the time, what circumstances Paul was addressing there, and so on. But we should keep in mind that a document sent out involves at least two communities. In addition to the community in the location the document is sent to, like Corinth, we should also think about the community in the location the document came from.

1 Corinthians seems to have been written by Paul while he was in Ephesus. So, in addition to his expectation that the Corinthians would be familiar with the resurrection appearances he mentions in 1 Corinthians 15, there's also a likelihood that the Ephesians would have heard about those appearances in the context of Paul's composition of 1 Corinthians. To the extent that they'd heard about the appearances before then, the circumstances surrounding Paul's letter to the Corinthians would have reinforced what the Ephesians had heard previously. And they would have had opportunity to get further information from Paul about the appearances and related matters.

Look at 1 Corinthians 16, all of the individuals and multiple churches mentioned there ("the churches of Asia" in verse 19, etc.). Or look at the similar comments in other New Testament (and extrabiblical) letters.

We should think of at least two communities when considering a document like 1 Corinthians. That's true not just with regard to the contents of the document, but also other issues involved, like authorship and genre. That means a larger number of people, accordingly, would have been well informed about such issues from the start. It's not as though a matter like who wrote 1 Corinthians, the gospel of Matthew, or 1 Peter, for example, would have been well known only to the author and the original recipients of the document. There likely would have been at least two communities who were well informed from the beginning. These documents were a means of informing multiple groups, typically groups that were some significant distance apart geographically. So, there was some diversity built into the circumstances at the outset. For more about topics like these, see here.