Uni has Grade 2 in both legs, but only once did I catch her lifting her leg, which was after a day running in the sand at the beach. She wouldn't walk after that for a day, that's how I found out. I started her on Cosequin then and had her on it for years, but I stopped giving them, as I didn't feel her knees popping in and out any less. So for about a year now of her not being on them, she still hasn't lifted or favored a leg.
Scraps on the other hand, I will start him on them and see if there is any improvement. He walks with a noticable limp and favors his right leg, even when he goes to lay down you can tell his left knee bothers him.