I think a lot depends on the dog. I had a Shih Tzu that I raised from a puppy. I had to rehome her when she was five years old. She was always afraid of new people so I was a little concerned about her settling into a new home. I found a good home for her and about six months later, I stopped by to see how she was doing. She completely ignored me, acted like I was a complete stranger. Even when the new owner handed her to me, (she would not come to me) all she wanted to do was leave no matter how much I talked to her. This really shocked me as I have sold puppies and seen them months later and they remembered me. She obviously loved her new owner as much as she had previously loved me. I am glad for her sake that she was happy in her new home but thought it really odd.