Do factory equipped vehicles always have same size drums front/rear?

My Chilton's Dart & Demon Repair & Tune-up Guide 1965-1972 page 205 shows 1970 6 cylinder cars had 10" front drums and 9" rear drums. All other years had 9" drums front and back. My 1970 Dodge Challenger Dart Service Manual page 5-54 also shows 6 cylinder Darts had 10" front drums and 9" rear drums.
My Chilton's Valiant Duster Repair & Tune-up Guide 1968-76 page 183 shows 1970 6 cylinder cars had 9" drums front and back, however, 1973-76 all drum brake cars had 10" front drums and 9" rear drums. For some reason 1970 Dodge and Plymouth A-bodies were different in 1970. I don't know for sure but 1973-76 Darts were probably the same as Valiants and Dusters.