My suspicion is that many of these books were written a few years before the earliest versions we have.
It may well be that the earliest church leaders knew Jesus or the immediate disciples and when that generation died off… it suddenly dawned on them they needed to copy the earliest manuscripts.
I think this, too, SamBee. And I think the versions we have may be slightly different that the originals (a la versions of the first vision) and/or may be retelling of the stories by others (probably relatives) of the people to whom the books are attributed.