I suspect that in some cases the elders might be gungho on catching a person committing adultery so that a JW can be free to marry.
It really isn't that difficult for the elders to track someone.
Take me for example. Let's say I divorced my JW husband. He had been an elder before I left him. Let's say that he had no grounds for a scriptural divorce (he did but let's pretend he didn't). I have custody of our children. (they are grown now but let's say they are still minors) I choose to move to another city for work.
He wants to remarry but must catch me in a compromising situation but now that I have left the home Cong he can't easily stalk me. But because we have children he has to know where I live. It is a really simple matter to get my address either from the kids or a lawyer. He does have rights to them so legally I have to let him know where his children are.
Elders in his Cong contact the elders in the area I have moved to and the surveillance resumes.
If a person contacts the cong where they now live they ask which cong did you come from. And they will contact the old cong to get your records. Especially if you were DFed they will want to get the scoop.
Your record follows you everywhere.
The WTS/JW don't believe in privacy rights. Let's face it the only rights they lay claim to are their own.