Someone correct me if I'm wrong, but I don't think any two separate recorders will ever record the exact same file length. They may be very close, but never exact.
Is that just what you're wondering about? If you use separate recorders you will generally have to do some time stretching/shrinking of one of the files to line up separate sources of the same show. Some people have claimed to be lucky and only had minor drift after a hour or more, but that has never been my experience. Especially after a three hour show, I find it hard to believe two separate recorders would be recording in sync by the end, with only a dropout to create a new file causing the latency.