There could be other reasons, like you mentioned including events from certain movies. I forgot about those, perhaps partly since it isn't a think kids should hear likely.
Another option, thought it makes things more complex, is to say certain movies happen on LBT earth 1, others on LBT earth 2, may or may not need an LBT earth 3. I don't think in these terms since, like I said, it makes things pretty complex. Though you'd have to be old like me to think of that or understand what earth 1, earth 2, is, since they were wiped out in the mid 80's story in dc comics.