That is the right answer. Transmission Fluids are 'backward compatible' except in a few rare circumstances. (Kinda like Dino Oil / half & half and 'New Oil' - synthetic).
BUT...it is not true for fuel!! Early (1950 to mid 70) gas engines needed the additives -LEAD & stuff- that are not present in current fuel. If you drive a 1950's car, (as you know) you need to purchase and add LEAD to your fuel for that car!!