I've been reading an outstanding book entitled, Jesus and His World by Craig A. Evans. Among other things, Evans points out that many of the Dead Sea Scrolls found at Qumran were two to three hundred years old when the community was destroyed! Evans also points to the work of George Huston who studied manuscripts from "libraries, collections and archives from late antiquity" and found that the manuscripts "were in use anywhere from 150 to 500 years before being discarded. In fact, one of the major ancient biblical manuscripts, "The fourth-century Codex Vaticanus (B)" was still being used 600 years after it had been produced. The point Evans makes is that "It is possible, perhaps even probable that the autographs of Matthew, Mark, Luke and John were still being read and copied" when the copies we now have, like P45, were being copied (75-76).
Take, for example, the Gospel of Mark which was written sometime between about AD 50 and 70. The earliest surviving copy of Mark and the other Gospels is P45 which dates to about 220 CE. We should not imagine that there were dozens--or even a half dozen--copies between the original Mark and P45. Evans' point is that it is "entirely possible, perhaps even probable" that the original Mark was still in existence (and could therefore be checked for accuracy) when P45 was copied.