I tried to find an answer in existing threads but couldn't find any. The only thread with a similar question I did find is about adding characters who only appear in flashbacks or as shadows and have a non-speaking role. So here's my question:
Should characters be added to an issue if they only make an appearance on the regular cover/variant?
I would say no in both cases: regular and variant covers. Many covers are misleading and have nothing to do with the actual story and in such case, the character should not be added to that issue as he/she isn't part of the story. It would be pointless!
Cable and X-Force #7 (2013)
This is one of those useless variant covers labeled "Many Armors of Iron Man" that seems to be promoting the upcoming movie, I think. I don't like these unrelated variants to begin with.
In the story neither of the 5 characters - FFF, Iron Man, Living Laser, Mandarin, Titanium Man - makes an appearance, nor does any armor of Iron Man.
However, someone added all of them to the issue; plus "Many Armors of Iron Man" as concept.
My guess is someone tagged these characters without even reading the comic, assuming they would appear in it whatsoever.