I think of the operative term as "doubleword consistency" (it is implied that the doubleword is on a doubleword boundary). That is why LM of two regs from a doubleword gets you "consistency", but "L from 1st word followed by L from 2nd word" does not). And yes, for the most part, it doesn't have to be 8 bytes, just something that does not cross a doubleword boundary. I never remember whether some of the moves for some lengths <=8 are an exception.
But few things have "quadword consistency" (e.g., LPQ, STPQ). LMG of two regs does not. Peter Relson z/OS Core Technology Design
