Fenderek: Good questions - the truth is I can't give any guarantees. As far as I know, there are no other copies of a "Hangman" studio version.
This information is also coupled with all the denial's coming from the Queen camp. Ofcourse, I can not pre-empt QP, (nor can I assume that they are liars), all I can work on is from "best information available", and state that the source of this info - comes from Queen themselves. (I believe that GB is on record as saying it does NOT exist. Try a Google search to find this).
To add some further weight to this position - I have first hand experience from the Freddie box-set, that without my contribution some tracks on that set would not "officially" exist. Other tracks, still don't.
(That is NOT a brag - but meant to be an honest answer to an honest question).
So - without access to the archives - or not knowing what other folks have in their collection, I can only act on the most reliable information available and act accordingly.
All I can say is that "if" another "Hangman" turns up then that may well be released. But I honestly think that the chances of that happening are very slim indeed.
"Listen to them. Children of the night. What music they make."