I live in another country but all the jws in the area know who I am. The "family still in" tell the congregation secretary. He tells the bethel. bethel contacts the bethel in the new country. That bethel contacts the new congregation. and........ the new congregation sends an elder to see you, normally around the memorial time.
So, one came to our door. Unfortunately for him, Mrs P, I swear she has some Klingon blood in her, answered.
" Some of your husbands friends from his old country asked us to pass by" he said.
He never did get alot further, good old Mrs P LOL.
So the moral is: they will know where you are, and it will be noted on the new territory file.
Then of course, if your family don't know where you're moving to, well what can I say.... " enjoy yourself"