The Rabies I think is state law here {Tennessee}. I don't board them and usually in the winter is the only time they leave the house with us. We take them with us only when outside Temps allow it.
Rabies is kind of an issue in these parts. I have Coons, Yotes, Bats, stray dogs, etc to contend with. I'm in a rural area. Coons and Skunks are usually biggest Rabies risk. Possums are safe though LOL.
I’m in northwestern North Carolina, so the threat of contact with rabid animals is little different. Immunity is immunity, hitting them with more vaccine than necessary is not necessarily helpful, especially with older, weakened or sickly dogs. As I mentioned, I’ve paid for blood titer to establish that there is no need to vaccinate in the past. It can take a toll, on elderly dogs in particular.
Maybe there are differing types of rabies vaccine? It’s every three years here, after first vaccination at eight weeks and a booster about three months later.