But in this case flashback shows what how Peter ended with May and Ben which is important. I think that all "revealing" and backstory flasbacks should be in. Only those repeating something we already know and seen should be out.
If You don't agree with me You should remove all: Princess Fen, Leonard MacKenzie and Thakor (because they were dead long before FF1) and You will have giant problem with most of 1990 x-men issues beacuse they are one giant stream of partial flashback issues revealing and revealing and revealing and changing and changing and revealing....
but generally flashbacks inside of an issue should be out
Sorry for strong words but to me that rule is stupid - it shouldn't matter if it's inside issue, outside issue, 2 issues, half issues, one page, two pages, 7 panels - it should be about importance for character backstory, and not about lenght. Sometimes one page of characters flashbacks is more important than 4 issues of story ( check Avengers Annual 10 vs any Avengers issue in 1967-1968)
One more thing: theres one example which shows how confusing that kind of listing can be is Changeling in X-men. You included him in X-men 41&42 (which creates spoilers) but not included him in X-men 65, so people never really found out what was he doing there. If someones reading by the changeling appearances knows nothing, seen nothing, learned nothing. Foul.
I always thought that those appearances were for people to read all issues and whole story of a character. But now it appears that I was wrong. At this point I really feel I don't uderstand the point of Comic Box.