I wonder why your vet wouldn't order singles for you...
Ellie has been titered the last two times. I'm not sure what we will do this year yet. However, from what I have seen of titering for Ellie so far, I'm not impressed. IMO, while it "may" be better than nothing, doing puppy shots, one year boosters, and then titering every one to three years is far from the perfect protocol.