hmmm... back when I worked at the vet clinic, the 3year rabies was a totally different vaccine. I don't know what the difference was but it was in a totally different vial. Most people didn't know about it anyway. Frankly they didn't need to. Lord knows some animals never went to the vet for anything other than vaccinations. At least they got a checkup when they came in every year. Plus the registration tags were only good for a year anyway.