Honestly, I'm kind of surprised that your vet chose Celebrex as the treatment...I believe I commented on your prior post, and stated that it didn't at all sound like Borna Virus to me, but rather a neurological issues/spinal cord issue, which is exactly what it is if the Celebrex has worked. I mentioned that if you didn't want to do imaging tests to find out exactly what the issue is, then your vet should try either anti-inflammatories and/or corticosteroids...While I'm glad the Celebrex helped him, I'm just kind of shocked that this was the choice of drug, or that he's suggesting that your bird should be on it long-term, and I highly suggest you get a second-opinion from another Certified Avian Vet soon.
The reason this is concerning is because Celebrex is an NSAID, and a Cox-II NSAID at that...Celebrex and pretty much all other Cox-II NSAID drugs are well-known to be dangerous when taken long-term, as they have a very high incidence of causing heart attacks, strokes, blood clots/aneurysms, and then also bleeding ulcers in the stomach and intestines, as well as bowel perforations. All of these are extremely common with the use of Celebrex, so for that reason it's typically only used for acute arthritis pain, and then a safer arthritis drug that is not an NSAID is typically used daily over the long-term...
I know that you're extremely happy that your bird is back to his old self, but the only reason he's back to his old-self is because the swelling, nerve impingement, etc., basically his pain has been relieved by the NSAID, and there are many much safer drugs that he can be given that will do the same thing for him and that are meant to be used continually over a long period of time...Celebrex isn't that drug...I wouldn't ever give any of my birds, my dogs, or myself Celebrex for much longer than to get their immediate pain and disfunction under control, and then I'd discuss switching them to a much safer maintanence anti-inflammatory and/or steroid or pain med...but not a Cox-II NSAID like Celebrex, which has such a massively high incidence of potentially fatal side-effects. (And those are in people and dogs; the thought of keeping a little Green Cheek on it for very long is very scary to me, as there wouldn't be much at all you could do if a serious problem did arise)...I'd highly suggest you get a second opinion from another CAV soon, as you do not want your bird on the Celebrex for a long period of time...
I am very happy to read that it has helped your little one out significantly!
