If they're the rightsholders, they can do whatever they want with their IP, including changing licensing terms, adding contractual obligations forbidding certain types of use, forbidding sale, etc.

I feel like that would bounce hard off first sale doctrine. But what do I know.

You still have to adhere to license and copyright terms after first sale.

You can't sell a Bluray disk to a movie theater and give them the right to charge an audience to watch it in the theater later.

If rightsholders are worried about certain uses of their IP being found to be fair use, they might then change the terms of release contractually to stop or at least partially prevent training.