I think a lot more JWs left after 1995 when they first introduced the overlapping generations. The year books indicated something like 200-250k per year being missed , I think it was worse then that and the number of ones coming in was far less then the 250-300K per year they stated.
After 1975 they lost a lot then rebuilt till 1995 then loss more and have never been able to regain those losses because of the Internet which also went mainstream about 1995.
Another thing to consider about Rattigan’s Numbers , he says they now have 304 congratulations listed in his state but how many of those are foreign language congregations that are only there because a bunch of English speaking JWs are supporting a small handful of people speaking a different language. They in all reality probably have far less then even the 304 they list. Their bleeding like never before!