I've just used the Celebi Egg trick twice on cartridge (Crystal) to get myself a Celebi, and then a Mew. No issues encountered, and pretty straightforward. I went to check DVs using an online calculator (w/ rare candies) and noticed that both of their stats are a bit strange; they get flagged as 'out of bounds'. In fact, they're almost normal, but the speed is a tad higher than it could possibly be.
For instance, my level 6 Mew has:
- 28 HP
- 17 Attk & Def
- 18 Special Atk & Def
- 20 Speed
However a level 6 Mew cannot have 20 Speed without any Stat Exp (regardless of its DV), which mine doesn't. The 'impossible' stat on my Celebi is also the Speed stat.
This got me wondering how the egg's DVs are determined in the process of doing this glitch. I couldn't find much information on this but I'd love to hear from anyone who knows about it! Perhaps this will also explain why the Speed stat is not right in the outcome as well.