May of 1997 saw Marvel Comics become weirdly interested in its own history. So interested, in fact, that the entire line was hijacked for the month cover-dated July for "Flashback Month," with every single title telling a one-shot story set before
the first issue of the series (and, in many cases, before the Fantastic Four had launched on their fateful rocket flight).
This was more of a problem for some series than others, leading to a number of surprising additions to Marvel canon, whether it was seeing Peter Parker's parents in action as spies, a child abuse storyline for Flash Thompson, or discovering future X-Men villains eking out a living in carnivals across America.
Each issue had a Stan Lee introduction (or, at least, a Stan Lee character introducing the action) and a distinctly more 1960s retro vibe than was usual for Marvel in the late '90s. Looking back on it a decade later, Tom Brevoort described the month as "ill-advised," because in his words, "many readers don't really want an entire month of comics in which their favorite characters have no costumes or powers, and the #-1 numbering allowed many of them to simply skip over this month's issue without leaving a gap in their collections." Some of the creative choices made in order to provide excitement for the month possibly helped the decision to skip the books, as well.