For me, Classics-verse means new modern toys for the original Transformers universe. That universe includes any and all characters that we saw in comics, books and cartoons from 1984 to 1995. I see no reason to draw the line at "G1" because the characters in G2 were the same characters separated only slightly by time. There wasn't any other 'universe' (despite the cartoon/comic differences) until after Beast Machines.

I do draw my arbitraty line at the start of Beast Wars because the several hundred year gap in the story makes it easy to see the Beast Era as a separate thing. Plus those toys are already in a more modern style. I like Henkei Dinobot but he doesn't fit on my classics shelf.

Retrofitted characters? Well Drift I'd include because the IDW take on the G1 Universe is the only place that character exists (in any significant way) so I'm used to seeing him alongside the Classics toys (see AHM etc). ROTF Lockdown (despite IDW comic appearances) and RTS Lugnut (despite the pack-in comic appearance) are too notable as Animated characters and their toys are movie-verse designs. They just don't feel right to me.

Fracture's a funny one too, but as her notable original character comes from the right era, and an era where Female Robot toys were the exception, and the toy (along with her wave partners) weren't really movie toys, I include her (whereas BugBite is case of "who?" and "why should I care?").