I am suggesting that the knob with the aluminum insert was used up to 1976;
I am suggesting that the knob with the slightly raised acrylic insert was probably used through 1978;
I am suggesting that the knob with the flush mounted acrylic insert was likely the last version, used 1979 through 1981.
I believe that as far as the rubber encased knob sub-assembly is concerned, it changed around or prior to 1979 - so all knobs prior to that had the insert sitting up;
I believe your second post, fourth image (below) is the first design knob sub-assembly used through to 1978(?)
I have one NOS three speed, and two used four speed knobs which do not have that raised center.