A quick search through our host's catalog, shows that you are correct.
But It does not explain why most 944s have the 968 knob. One might think it's because they break and are replaced with the new part, but my original manual from 86 shows different knobs on different pages.
Very Strange!
Anyways I think we have beaten this dead horse, to...death.
PS: Knob 944-613-535-00 is $0.75 cheaper, and yes they are interchangeable.