What I find interesting is the fact that the number of partakers has been around 8,000 for the last 20 years!! It does not appear to be changing.
Obviously if the majority of these were persons were actually baptised before 1935, they should be dropping off at a much more rapid rate.
Somewhere I have a list of the GB members, age and date of baptism. I'm sure its on the Net too. There are only a handful of them that were baptised before 1935.
As someone mentioned above, I think they increasingly rely on the ignorance of the average JW.