Not changing the address when a family moves unfortunately is common place, we often have instances of it. and usually after much phoning around find the owner, one was even now in New Zealand. One of the most memorable was, when we had a cat handed in that was in a bad way that had been found on a main road in Chesterfield it was taken to our vets where it received medical attention and was found to be blind, although it was micro-chipped they could not trace the owner so they asked us if we would take it in. The telephone number and address were in Kent, I contacted the Cats Protection nearest to the given address and they went to the house and found out that the family have moved out over 3 years ago and no one knew where. The surname was unusual so I logged onto Directory enquiries for the Kent area, no luck, so I then looked in the London area and there were 2 families listed with that surname, I rang them both but no luck, I had of course looked in our local book, I then rang directory enquiries and asked if anyone with that surname was listed as ex-directory, wonderful there were another two families. I explained the position and asked if it were possible for them to ring the families and ask if they had come from Kent and had lost a cat, of course you know the answer. I then decided to ask the local paper if they could put an appeal in. A while later I received a call from one of the office workers, she actually knew a gentleman with that surname through his work with the children of Chernobyl and would ask him to ring me. Yes, it was his cat who had been missing for about a week, a few days before she (now we know her name is Sophie) had disappeared, Sophie had a stroke and the family thought she had gone away to die, (I did explain that was an old wife's tale) Sophie was not blind the last time the family had seen her so perhaps she had been involved in some other sort of trauma.
Apparently there are only 8 families in the country with the surname, the owner still works in Essex but lives in Chesterfield, he advised me that he thought the new vet (who was not our vet) would have automatically informed the micro chip company of his change of address.