You're correct. Roy Thomas Baker originally mixed a 5.1 version of A Night At The Opera and it was released in 2001, but apparently Brian didn't like it and that version was withdrawn. A new mix, that Brian supervised, was released in 2002.
The 2001 mix has much greater separation of the instruments, so it's very interesting to listen to the separated tracks. It's very difficult to get hold of these days, as it was only available for short time.
My email address is below, by the way.