According to Kurt Busiek, Marvels was written with the assumption that all of the stories took place more or less when they were written. That is why the setting of the middle two issues looks like the 60s and why Sheldon's daughters aged by a few years between Issue 2 and Issue 4. Marvel, of course, never officially recognized the real-time aspect of the story (since it would raise all sorts of questions about Marvel's current-day continuity). From what I understand, their official line on the subject was that Jonah Jameson seen in the first issue was either JJJ's father or grandfather (I can't remember which atop of my head).