I only know what the Paramount exec told me, and he was in a position to know. (This was somebody for whom I did a lot of work over about a 7-8-year period.) I think you could go back and look at thousands of 1960s TV shows that lacked a © mark at the end of the show. I can recall remastered shows where they went back and superimposed a video copyright notice in the end credits, but they were basically re-asserting their rights that already existed on paper, kind of a belt-and-suspenders approach. I'd have to see a test case with a decision where a judge ruled that a show was not actually copyrighted because they left out the © in the end credits. I think this is a technicality, and they would rule the other way provided the show was actually copyrighted in the U.S. Patent & Trademark office with all the forms filled out. (I have warned filmmakers before: be sure to put the © on at the end, the "All Persons are Fictitious" disclaimer, and file the paperwork with the copyright office just to be absolutely sure that you're covered.) What is true is that there are a ton of 1950s and 1960s shows whose copyright is under a cloud, and because the copyrights were never renewed (and there was no © in the end credits), you could assume that a lot of the shows have slipped into the public domain. Stuff like this makes studios and networks reluctant to release old material, because somebody else could just grab it and re-release it as P.D.