Yes, drop and add, that’s right! I was somehow in a calculus course and couldn’t drop it fast enough!
I came to UF as a faculty member in 1985, and they continued using it for registration for a couple of years after. It wasn’t just drop/add, it was the entire registration process
1993 they were still using it. Using overhead projectors to show which sections were already filled. You had to keep the catalog with you and make some backup plans as they listed more sections that were no longer available.
I was a student at a different university in the mid to late 60s. Registration was at the “men’s” gym. They had huge list of course sections on bulletin boards, and when one would close it would be crossed off so you could try to make adjustments before entering.