Do keep in mind that the court didn't change anything, it rejected the challenge to a 1994 law that was passed to support an even earlier treaty. I don't like the law or treaty any more than I like the CTEA (the entire point of having different countries is, in fact, different laws), and do think the court made the wrong decision because the changes harm security for small businesses, but the ship has sailed and all those works have been formally under copyright for at least twenty years, no matter how many people used the characters or asserted that the works are public domain.
Prior to that, the courts made it absolutely clear that this was going to happen, anyway, with the Tolkein case being the clearest: Too many unbound copies were imported to remain "unpublished," so the original American edition of the books should have been public domain. The publisher who asserted it, though, was stopped because the courts didn't think that foreign works should be required to lose copyright for not abiding by formalities (even though that's the point of formalities...).
In fact, the 1922 date has never really been as firm as a lot of people pretend it is. That date is only for works granted United States copyright protection, with foreign works only vaguely governed. Different cases have had different results; depending on the district/state, European copyrights held or they didn't. In some cases, they were considered unpublished, which has its own, independent copyright term.
My understanding is that the only date you can be absolutely sure about in the United States (if you don't know where it comes from or know it doesn't come from the States) is 1909. Nothing published prior to 1910, as far as I know, has any copyright protection, regardless of where they were published. I don't know how that interacts here.
What's also still unclear is what happens to works published in the United States with valid copyrights that have expired. I believe they're still public domain, because that was the contract made, but you never know.
