MS-DOS didn't exist prior to PC-DOS, initially. "IBM's implementation of MS-DOS (PC DOS)" was the gold standard.

all of it came from QDOS, a CP/M-like OS M$ bought based on hiding their plans, and that IBM made PC-DOS from. PC-DOS shipped with the original IBM PC.

MS-DOS only became a thing once there were "IBM PC compatible" clones. It was very smart of M$ to see that coming. They kind of rode IBM's coattails into dominance in the market. Back then, personal computers were oddities and when IBM entered the game, their reputation gave them credibility.