Sorry for reviving this very old threat, I came across it while googling about wondercard dates.
Aren't the Pokemon illegal if you don't edit the date received? What I mean is, the IVs and the nature are tied to the seed, which is generated off of the date you booted the game. So if you inject, for example, the Meloetta that OP posted about, then it cannot possibly have the IVs of a different date, no? Or could you, back then, get the wondercard (which then has the old date you received it on as part of the Pokemon FOREVER) but reboot your game and reset for one you want? Are the Pokemon's IVs and nature generated off of the receiving of the wc, or will they adjust to your boot date?