Just as Esquires were routed for a neck pickup, even though they didn't come with one, my best judgement tells me. Musicmasters and Duo-Sonics shared bodies in the same way. Even though Duo-Sonics were not made not made in the '70's, Fender likely kept using the same old templates to cut the bodies. Or maybe even, through the '70's, they worked their way through a stockpile of bodies that they had originally milled in the '60's, when there were Duo-Sonics.
I am not saying that I am 100 percent certain...but I do know Fender's student guitars very well, and I've never seen one just like that. Exceptions do pop up with Fenders, though not anywhere near as often in the CBS years as during the Leo Fender years.