This might be one for John S Stuart to answer, as I don't recall it being brought up in the past, but are there different versions of 'God Save The Queen' on records? The reason I ask is that the band had apparently recorded the national anthem during sessions for Sheer Heart Attack, or at least one would assume, considering that it was played over the PA of their live shows starting in October 1974, but that a version was also included on the July 1975 US single reissue of 'Keep Yourself Alive'.
This begs the question: was 'GSTQ' re-recorded for A Night At The Opera (sessions for the album didn't start until late July), or was the Sheer Heart Attack version held back from that album and issued on ANATO?
I just realized that there is a vague possibility that this topic may have been addressed on the recent 30th anniversary edition of ANATO, but as I don't have that release, I can't really know for sure.