I encourage anyone interested in the statuses of copyright when it comes to theatrical cartoons to check out these sites:
Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine and
https://cocatalog.loc.gov/. This is where all of the information about this sort of stuff is held. I haven't scanned through all of them but scanning through them briefly, here are some observations I've noticed:
- Unless I'm missing something or putting in the wrong words, if I'm reading correctly some Looney Tunes shorts (Wackiki Wabbit, Yankee Doodle Daffy etc.) appear to have been NEVER registered even at their time of creation (as opposed to been registered and then not renewed like Molly Moo Cow). Thus, most of the later copyright registrations are their first.
- Most of the later copyright renewals for some of the cartoons that fell into the Public Domain are for alternate versions of them (ie redrawns, computer colorized versions, restorations etc.). Theoretically according to copyright law, this COULD protect those versions of those cartoons, but not the film elements before that time. A company trying to protect the original, untampered versions of these Public Domain cartoons would thus be disingenuous (though I'm sure there are some legal businesses I don't know about that they COULD pull to do that).
Funnily enough, sometimes companies mistakenly think that a cartoon they own is under copyright when it's really not. According to David Gerstein, some recent copyright documents list Wacky Blackout as being renewed alongside cartoons that WERE renewed, when in reality it was not.
(BTW, the main reason why these cartoons fall into the public domain in the first place is either A. The studio goes under and isn't around when the renewal is supposed to take place or B. Secretaries at a studio forget to send paperwork.)