Hi Karen

Your thread caught my eye, as we have recently had similar news

Only Abi is a stage III. Firstly, I want to say I think you're fortunate to have a wise vet. What kind of diet "change" did she recommend, and why do you decline? Is Cooper overweight? If so, I'm sure she told you that any extra weight will be detrimental in this case. I will say that Abi was a hefty 10lbs when she was most symptomatic. We cut back her portions, and she is now between 7.5 and 8lbs; which I will also state I'm NOT entirely happy about. I can feel every rib and vertebrae. I know she shouldn't be 10lbs for her knees; but, honestly, she looked much better. She is rather long for a yorkie, at 11" from neck base to tail base.
I, too, am blessed with a wise vet who sent us to an even wiser surgeon for consult. We went in expecting a surgery date for sure; and was pleasantly surprised when she said "no, not yet". The surgeon said she has patients with stage III & IV on whom she has not done surgery, because they are not symptomatic enough to interfere with thier quality of life. Also adding that she's had some stage Ones where she found surgery necessary because the dog was in pain every day. She treats the dog/case; not the book case LP.
We watch Abi to be sure her knees are not locking. We do not restrict her play activities. I, too, was worried about even walking her! She's only had one incident in the past few months (since seeing the surgeon) where one knee locked, and she hobbled to me for help

. I was able to massage the muscle around it and relax the knee back into place. If this continues regularly, we will, most likely, be looking at surgery.
Then, there's the friend whose dog had LP so badly he chased the mailman on three legs. But...he did not seem to be in pain, and his vet told my friend to NEVER let anyone perform this surgery on her pets. It ofttimes does not work.
So, I guess we are still left with our gut instincts. Best wishes to Cooper, and I wouldn't worry unless this begins to impede his ADLs (activities of daily living)