How many turn in deceptive or misguided field service reports will always be a question.
Counting numbers is more of a business way of keeping track. Since this religion is more of a corporation then a religion the numbers misdirect.
The Mormons list a membership of 18 plus million Mormons. But they get to that figure by counting every one who was born-in or joined the Mormon religion but turned inactive.
In the past....... JW yearbook surveys included.....Baptisms, Peak Publishers and 'Leavers'. Check the memorial attendance and deduct peak publishers and you have an idea who shows up once a year out of respect or curiosity.
Leavers could be JW's who died, or JW's who left the religion. The numbers I saw indicted that half of those who identified with the religion left it one way or another.
While you can still leave........ as long as you don't mind being shunned in one form or another .........prior to 1980........ a person who left without having committed a major sin simply left. Family and friends could stay in contact. The friendships usually faded, but family ties could be maintained.