This Rabies Jab article was fascinating

Check this out ; About the rabies jab and the blood test which is often done afterwards. The article is from a Cesar Milan "ask the vet" page.

Ask the Vet: Rabies Vaccine and Over-Vaccination

Can a dog get a rabies shot twice? I am waiting for the previous owners to get me the paperwork but they have not done so yet. If I never get the paperwork, can she get the rabies shot again?

If you do not receive official paperwork showing that she received her vaccinations then you should consider her vaccination status to be suspect. In this particular situation it is strongly recommended that you get her core vaccines up to date regardless of what the previous owner states about her vaccination status since the previous owner is unable to prove that she received them. The AVMA designates canine distemper, parvovirus, hepatitis and rabies as core vaccines. The recommendation for re-vaccination is for two reasons: 1) it will help protect your dog in the event that she was not really vaccinated and 2) it will protect you legally if you ever need to prove that she has been vaccinated for rabies. The slight risk of a vaccine reaction is better than the risk of leaving your dog potentially unvaccinated. If you are concerned about over vaccination then there is the option of asking your veterinarian to check her rabies titer to see if she is protected or not. Keep in mind that the titer test is fairly expensive, not always locally available, and can be unreliable. In most cases it is simpler to just vaccinate.