You are right, but one can also argue that since Harry and Lily were exposed to very different drugs/formulas than Norman, that the results to them and the baby were also different. But that should have been mentioned in the comic.
One can also argue that it was all an illusion, an there was really no baby at all. My point is that these are questions that probably doesn't even make a 'blip' on the writers radar while it is being written. Anything that isn't mentioned in the comic is up for interpitation, to anyone. There should be an editor in place, whose job it is to make sure the comic makes sense before it is being launched. All in all, most people on this site probably could, and would do a better job as editors than those the ASM tittle has at the moment. That way, there would be someone to say things like "When did Harry arrive?" or "Are you sure Spider-man should look like this? He dosen't look right". You know, being an editor, who does the editing.
~Epidot (and still blowing off steam).