This is more of a subset than a series, but it's interesting (and complete) so here it is anyway:
Around 1995-96, near the end of the Sega Genesis' life cycle, Sega inexplicably re-released 5 older titles in their original packaging, but with the addition of the new (and still current) ESRB ratings, as well as some changes to the manuals. This was strange because these titles had already been re-released in updated packaging during the early 90's. Games like Sonic & Super Monaco had been available for years branded in the "Sega Classics" packaging (first with Sega's rating system, then with ESRB ratings when it came along). Why Sega chose to go back to the original packaging for these few games is a mystery, especially since they had been available all along anyway. I'm active on some Sega boards, and nobody has ever heard of a reason why Sega did this. I was a huge Genesis fan during the 90's, and I don't recall any special promotion for these variations (such as "blast from the past" or anything similar).
These variations range from pretty common to quite uncommon. Super Monaco, After Burner & Taz Mania are quite easy to find, while Super Hang-On & Sonic don't come along very often. I've seen copies of Sonic sell for $100+, while Super Hang-On took me over six months of online searching to find. Seeing as Super Hang-On was a launch title in 1989, that makes it the oldest game - released during the original hardware's life - to be branded with the currently used rating system.
