Honestly... I don't
Harley got all of his shots at the time he was neutered, but he's gonna be 2 in June- and isn't up to date on his 'yearly' shots. Honestly, its becuase he's a HORROR at the vet. He hisses, and gets really scared, I'd rather not put him thru that. He goes to the vet when he's sick - and I took him this spring when he had a temp/cold- and he got meds, but otherwise they said he was healthy.
Bayley is the same way. He doens't appreciate the vet, and I'd rahter not put them thru that.
They are both indoors, but I take them out sometimes when its nice on their collars/leashes.
I think there are some other members that don't take theirs in for their yearlys either... as long as my boys are healthy, I think they are okay. My vet even said that not even takes their indoor cats in for their yearly visits. I think its somewhat 'normal'?