Ah. This probably explains why they can't remember. I mean, bad on them for not having this information charted SOMEWHERE - we put the vaccine labels in the chart, write down the injection site, and log it in the computer - but at this point they're probably never going to remember if they gave a shot or not. I can probably remember what we did with all the patients I interacted with today, but even the specifics of yesterday are foggy.... we just see too many animals, give too many injections, that it's hard to clearly remember who received what if it's not brought to our attention asap.
They should certainly be able to tell you exactly what was done at your appointment. Do they acknowledge that your cats received ANY vaccines at all, or are they trying to say they received NONE? It's a stupid situation because if there's no record of it happening - then it didn't happen. But I would not be quick to give the rabies vax again if there is any possibility that they already got it.
However, I will say that it does worry me that there is the possibility the kitten didn't get it. I wouldn't want a kitty that young possibly going unprotected for a whole year. I would think a rabies titer on a kitten would be pretty telling, because if the antibody response is sufficient.... well, why else would that be unless they had been vaccinated? Rabies isn't exactly one of those viruses that you come across frequently enough in your day-to-day life for the immune system to build up its own response. I'd get an opinion from another vet clinic.