That's the crossover era from clear interiors to Granitone. It's probably original from the factory.
Presumably, Granitone was used to hide less-than-pretty interior plies. It wasn't the first time it was used. Ludwig also employed it on the Standard sereis a few years earlier, to hide funky work. The use of "seconds" for the shells of the Standards was part of what enabled the reduced price of the series.
Back in those days, most players weren't concerned with the minutia, and could care less if the interior of one drum looked different from the other. Remember, it was also an era where more drum heads were opaque. It was an era where the ONLY thing that counted was the SOUND, which is really the way it should be.