Both of the previous atttoeneys have provided good advice. You said you adopted the dog. If the dog was adopted from a government body like the Tulsa City pound, there would have been a time frame for claiming the dog before it was available for adoption. this more than likely will invalidate their claim or make it more difficult to recover as the City will have some ordinance that provides for forfeiture of the property (the dog) if not claimed within a certain time frame.
Answers to AVVO questions are for general purposes only and do not establish an attorney-client relationship. This answer is not a substitute for legal advice and should not be relied upon without a full consultation with an attorney that can fully look at issues involved.
The absence of a scar suggests that:the animal you have:
1. Is not the one they lost; and
2. Should be spayed.
Since the physical evidence apparently does not support their claim, there is little more you need to do at present - except spay the dog. This will do two things:
1. Do what should be done anyway, unless you are breeding registered shih tzus - which adoption of a lost dog is incompatible with; and
2. Give YOU proof that the animal you have cannot be theirs, as you cannot spay a dog twice. Your vet's record of treatment would trump their claim, which is based upon their losing a spayed dog.
The foregoing is for general information purposes and does not establish an attorney-client relationship.
I agree with my colleague - though not every spay produces a scar. Your vet can confirm if the dog is spayed. I'd also make sure the dog is registered in your name and microchipped. I'd then tell the people that claim she is their dog that they are going to have to sue you and if they do you will counter sue for her care for the time you have had her - including adoption fees, vet bills, food bills, and a daily boarding fee. Then ignore them.
If we do not have a signed fee agreement I am not your attorney and this is not legal advice.