This happens from time to time. We get an animal in that someone found or is a stray. So we scan them, find a chip, and can't find an owner.
The other day, a lady brought a dog in that she found at the Lehigh Valley Mall. A neutered, approximately 4-6 yr old Bichon Frise. Her friend actually found the dog, who supposedly was in some cage/crate (in the mall walkway? I don't know..she had no idea). Then her friend told her the security guard actually owned the dog but didn't want it anymore. I know, sounds hinky to me too.
So we scanned the dog and he had a microchip. We contacted the company, who sent us to the breeder from whence he came. He was chipped in 2006 (so my age estimate was right.) Some breeders will chip the dogs before they get shipped to a store, etc. The breeder sent us to a store in Florida (mind you, we are in PA here). We attempted to reach that number and it was out of service. Therefore, this young lady can keep the dog.
However, I will never know if maybe someone really lost their dog or had it stolen at some point in time and would want him back.
There is no point in getting the dog chipped if you don't register the chip. No matter what chip your vet or breeder uses, it is easy and inexpensive to do! You can even do it on-line. AND many sites will allow you to upload a photo, which can be very helpful if your pet gets lost. If you move, you can easily update them through the website also.
And one more thing: These microchips are NOT a tracking device. Your pet cannot be located on GPS with them. If a vet or shelter doesn't scan for them, no one would even know if your pet has one!