Your so right mate i reckon most ferrets found wandering about are the good workers who never had a collar on when they where ferreting
In my long time of ferreting, I have only come across one that was lost, I was out for a mooch with the dog on a flood banking, when i noticed a couple of rabbits bolting, soon to be followed by a Jill Polecat ferret, I was wary on picking her up, but she was fine,
Got her home, and worked her and she stayed with me, till she passed away, probably one of the best workers i had.
and she had no collar, when found.