Laura, I would say go ahead and change the year she graduated if you want. Why not? Just explain it in an author's note at the beginning that you know what you're doing & people should just go with it.
Lois's age on the series never made sense when all the pieces of the puzzle were put together (and neither did Jimmy's, but that's for another time.)
In the long (ie UK) Pilot, Lois says she's 26. In SuperMann we learn that Neverending Battle (and therefore The Pilot) took place in May (ie the newspaper headline; then the three nazis emerging to see Superman save the little girl from NB). Which means she's supposedly 26 in May 1993. So if she was born in 1967 (as Tempus Anyone? tells us), she could not ALSO be a Libra (as she says in Contact) because that means she would have turned 27 in September/October... which she couldn't do if she was born in 1967 and this was still 1993.
Sooo my point is, do what you want, ok?
