A-904 Compatibility and changes?

The only thing I can think of that changed in the '71-'72 era was the introduction of the part-throttle kickdown valve body.
Many other changes earlier and later than that, though- the major ones are the input shaft size/spline pre-'68, pushbutton case (cable shift) and VB until '65, speedo drives changed in '67, ball and trunion (flange) output shaft until '65, Cooling line ports were increased to 3/8" sometime in the '80s (probably when they added the lockup convertor), lots of governor changes over the years, and probably lots more that I'm not aware of...
I have no idea why they grouped the years that way.