Pre-80 is a dumb idea.
Either:
Pre-75, pre-78, pre-81, pre-85 (while there are exceptions, this roughly translates as short-travel, medium travel, Evo, and pre-85).
or;
Pre-75, pre-79, Evo pre-85 (again, there are exceptions but roughly: short-travel, less-than-12"-of-travel, 12"of travel and pre-85)
The above does a far better job of classifying bikes by their broad technology groups, and keeping the groups roughly the same size, than changing Evo to pre-80.
The other option is to ditch the bike ages, and make the rules reflect the bike's original level of technology (in much the same way as Evo does). This has the advantage of removing the need for lists and the carry-over rule.
All of these have the disadvantage of putting people who have bought/built bikes into more competitive classes. Think of all the YZ250H owners, for just one really obvious example.