I think it is possible to have more than one Master. This is achieved simply by sending the signal from the console to more than one tape machine simultaneously. Each of these Masters would theoretically have identical sound quality as long as identical tape machines with identical set up were used. Each of these tapes would correctly be labeled first generation.
"Cut from the original master tapes"
this is a phrase I see often when looking at new vinyl of old recordings. I always wonder if this is a good thing. I'm sure the tapes used are of a better quality than the 8 track, casette, or reel to reel tapes that I used but were they really of a quality that they would still be Quality today? Do they not lose their muster, so to speak, like everything that one deems to be from that period of time referred to as "In the day" (yours truly included)?