In addition, if anyone has an older dog, they should also immediately look into Librela: https://www.zoetisus.com/products/dogs/librela/ This is a miracle drug that pretty much instantly changed both my (older) dogs' lives. Every vet tech I've spoken to (it's a monthly injection) agrees it is amazing.
He also loves the cold, and he's always more active in the winter anyway. I would say he's close to the level he was last winter instead of slightly declined. That's great, but not miraculous.
We'll stick with the regimen and see if he continues to improve. I'll upgrade my judgement if he starts climbing stairs again.