There was alot of growth pre 75 then in 1976 N.H.Knoor went on a world wide tour to shore up the masses as the number started to go down.
I went to his talk at the Auckland New Zealand Town hall,He spoke for 90 mins with out notes,Looking back i'm sure he had given that talk so many times he didn't need to.
It took a long time to recover from 75 and they gave a sort of very vague apology in a Watchtower in 1982 that by now they will be denying.
Karter.