Yeah, I don't know how Marvel handles details like that. Apparently they have their own alternate and parallel universes up and running (where 616 is like DC's Earth-One?), so maybe the early Silver Age issues are on their own domain at this point. Or maybe they just never bring it up, which is as good as a lengthy explanation with me.
All the retcons and revisionism always reminded me of Soviet history, where people were airbrushed out of pictures in textbooks because they had fallen out of favor. Poof, Comrade Trotsky wasn't at that parade, he never existed.