Hi there and thanks for your question.
The record of which vaccine goes along with that tag will be on the computer of the vet hospital who administered it. Unfortunately there is no other log kept anywhere else.
Your vet should be able to look up the tag number, combined with the year (should be on the tag as well) and determine when the rabies vaccine was administered.
However, a rabies tag alone is not considered proof of rabies vaccination as the tag could have come from another dog. The only recognized proof would be a rabies vaccine certificate.
It is possible though that your vet's office has had some type of mixup, so it would be a great idea to ask them to look up the tag number in their system to see if they can get to the bottom of this!
I hope this information helps! If you have more questions regarding this problem, just hit reply. If I am online I will respond right away. Otherwise I will respond as soon as I come online again. Or, if my answer is sufficient, then please hit accept. Thanks!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.