On the basis of what law or treaty? First of all, dedication is not "free licensing". It is not licensing in any sense whatsoever. When you dedicate the work, you are no longer the holder, hence public domain is also what works fall into when the author is long dead. I'm not sure what piece of law you'd be re-interpreting to reverse all of that understanding, which would be a precondition to allowing dedicators to retain any control whatsoever over a work that's currently in the public domain.

Your original point was better, if it is ruled that "dedication to the public domain" is not and has never been a real thing, then the original dedications never took effect, and copyright holders remained copyright holders instead of forfeiting all control. Stick to that one.