I believe that if you leave it in the day care then the moves it had when it was left get passed down and not the overwritten ones...
I'm not sure either, I think once the egg move is overwritten by something else, and the egg is generated after that event, then the egg moves don't get passed down.
What I do is pre-level to about evel 15 and then take the parents out after every new move is leaned and move the egg moves to the bottom of the list but this doesnt work with 4 EM.
Same here, it's really frustrating that at early levels, the egg moves get overwritten fairly quickly. This is why I take the long cut by having the parent gain levels in "Le Wow." What guarantees a no-overwritten egg move is if you get your pokemon to a level high enough that it doesn't learn any more moves which is what almost all 4 egg move breeders should do, unless one wants to go over to check each and every time, but it's too tedious in the long run if you plan to pass down all 4 egg moves.