It's happened to me several times. A few doors up had a kitten and five small children - the kitten often came to our house for sanctuary, so when they upped and moved and left her behind, we took her on. A few years later, a boy kitten from the other end of the road started to drop in - I was going to adopt him officially, but he found the three big cats too much competition, and took himself off to a new home. Our Black Spot used to live next door, and Rover's a stray who turned up in the garden a good ten years ago.... No. 1 Son's the only cat I actually chose from a litter!