"That "someone else" has not legally bought the rights to anything, and will certainly not even attempt to go to court regarding this."
I agree. IANAL and I didn't read past the the commercial license, but can someone sue, with a reasonable expectation to win, over an IP that was owned during production? Imagine the unlikely scenario where Disney sells the ownership of Mickey Mouse. Unless there's a clause stating that the purchase also includes owning rights to everything ever produced with the Mouse in it, I don't think the new owners should be able to claim ownership over previously made ip; they should only have the license for future productions.