I was cleaning the garage and um, discovered five 2 speed wiper motors.
Top row dated August 1964, November 1964, and December 7 1965
Bottom row dated February 1965, June 1965
I thought it was interesting all the '65 wiper motors were C4ZF-17504-B. I guess -A was much earlier than August '64.
They all looked same. The '66 wiper motor had an extra wire and was stamped C6Zf-17504-B. Maybe -B doesn't signify an engineering change?