I don't know if you still have the quad cart around but you may get to a point where it is nice to have just as a "standing frame", something to get him in an upright position for a while with no expectation of walking necessarily. He may get to where standing is enough. Though I think you have another arrangement where he can stand under the tree without a cart, which looks really good. My senior large breed dog was 13 and had a quad cart and by the time he needed the quad, he really wasn't up to going far, he also had a 13-year old heart and kidneys, etc., but it made him smile just to be able to stand in a normal position on the back porch and feel the sun and breeze on his face. He was only 62 lbs, which is less than your dog, but I was not able to sling him as well as you seem to be able to, or I would have done as you have been doing.
You know, you are kind of working with 2 curves right now? There is the neurological healing curve and the natural aging curve, and he is living at the intersection of the two. If he was 11 when he was injured, then he must be 12 now, and that is approaching the lifespan for a standard poodle. But the thing is, to me anyway, it all
matters. Every little bit he has got back this past year matters
to him, it's a gift, every atom of improvement, even if he is not walking. I hope the clock won't run out on him before he walks, nobody knows the future, but right now I am sure that on some level he can feel the improvement trend in his being even if he is working against the clock.
At this point, if he is beginning to feel his age, he is aging loved and in good spirits, that is everything
. To me, everything you have done, the therapy, the exercising, brainstorming for more ideas, selecting a cart and tweaking it and fixing it, the right sling, the right boots, giving him the time and care and companionship, the physical aspect of dealing with a 95 lb dog, many things you do not mention like cleanups and bed changes and laundry, and all the things that go with having a large down dog, it all matters.
I once heard a story of a pioneer family of 3 generations who got in a covered wagon and set out to go west. Halfway across the prairie one day, the grandmother sat down under a tree facing west and breathed her last. She didn't make it, but she was still looking west when she passed. And your dog is going to continue to do what is natural to him, recover a tiny bit at a time. He is happy trying even if the ultimate goal is not a guarantee, I don't think you'll ever regret that you set out on that journey together.
And if you asked him, it is possible he might say this has been one of the best years of his life, because of the time you guys have spent together. He is probably not thinking, "Boy I wish I could run around the yard", he is probably thinking "When is my buddy coming home and what will we do today?".
It's just good. It's the definition of good.