I know it works that way in gen 7, but I'm wondering about gen 4 specifically because I traded for a shiny Manaphy that PKHeX says was received as an egg on the first day the egg was available, which seems suspicious. The Manaphy egg is shiny locked on the receiving game and can only be shiny if hatched on another game whose TID/SID make the egg's PID shiny. It's highly unlikely someone attempting to hatch a shiny Manaphy managed to get a desirable ID combo the same day they got the egg, so unless the egg keeps its original received date after trading, I'm very doubtful of the Manaphy's legitimacy (or at least the legitimacy of the original as mine is cloned). Unfortunately I have no way to check myself as I sold all my old games.
