Does anybody remember that at one time the Great Tribulation began in 1914 and it was cut short about 1919 for the sake of the holy ones (can't remember why). There was to be an interruption for a short period of time, then the Great Tribulation would start up again as Armageddon. Except the "short period of time" became a long period of time. So they changed the explanation that the Great Tribulation was in the future and was one in the same as Armageddon? I think the explanation changed in the early 1970's.
So I think the explanation was that the Great Crowd came out of the Great Tribulation that had already begun.