You have said, “I believe the Rapture is based on reaching a specific number of believers rather than a specific date.”
You keep saying that as though it is mutually exclusive; the number comes in on a certain day, and on a certain day, the number is full.
By specific date I mean a previously known date like the date of a particular feast. Obviously, since the rapture will happen in the context of time it will happen on a certain day. But, it will be the day when the church reaches its full number, not a day that anyone could have known in advance.