**The info is from my vet, who attends conferences. Somewhere out there be the paperwork, may or may not be published publicly on the internet.**
Vets say a lot of things, often they say incorrect things too. Been there.
Remember, the only way to determine immunity is through challenge - titers only measure circulating antibodies, which may be low in spite of the dog being protected. We have no way to actually measure if the dog is protected except by exposing them to the disease. Titers are the next best thing, but still inadequate. In dogs that are not around other dogs or dog events, I actually would expect titers to be low.
Keeping the dog's immune system up and primed for certain diseases (like parvo, not life threatening in adult dogs), can prevent it from serveilling for other diseases, like cancer or tick disease. In my mind, those are bigger risks in our senior dogs which may or may not be exposed to these other diseases and most like have the memory cells to protect them.
But owners will make the decisions that they re comfortable with, these can be very individual decisions.
Sorry SW, didn't mean to hijack!