redflower1,
Certainly, a carpal tunnel release (CTR) can fail.
Usually, the most common reason for a CTR to fail, is that the patient did not actually have carpal tunnel syndrome in the first place.
However, if the patient had electrical studies and exam consistent with significnat compression of the median nerve, then a failure of a CTR has to be evaluated as to when the "failure" occured.
If the patient has absolutely no change in symptoms after the release, then usually there has been an incomplete release of the tight structures over the median nerve. It usually means that there is still a tight band in the forearm or at the distal edge of the transverse carpal ligament (the two most common places to miss a tight band when doing a release). It is more common for an incomplete release to be done during an endoscopic CTR, than during an open release, but it is still possible in both. This is usually a pretty easy problem to fix, just finish the release, making sure to release all of the tight fascial bands.
If the patient has a period of relief of the symptoms after the release, but then the symptoms return, then usually the cause is the formation of scar tissue around the median nerve. Unfortunately, this can be a very difficult problem to treat.
If the patient has formed scar tissue around the nerve after surgery once, then just doing the surgery again will usually not take care of the problem, it usually makes it worse (the patient just forms more scar tissue). There are some procedures which can be done, to protect the nerve, such as wrapping the nerve in a vein graft, covering the nerve with a fat graft, or using a silicone sleeve to cover the nerve. But, again, unfortunately, the results after these procedures is usually just not as good as a primary release.
As to the trigger fingers, they could be related or totally separate. Some patients develop a lot of inflammation, swelling, and scarring after hand surgery. If so, this can lead to inflammation and swelling in the flexor tendon sheaths, which is what causes inflammatory tenosynovitis (trigger finger).
Usually, trigger finger can be treated easily with injection(s) of steroid into the tendon sheath. In the 1% that do not respond to steroid injections, then a release of the A1 pully can be performed.
But, since you have had four hand surgeries, it is very important to determine how much the median nerve is now affected. Then, you and your surgeon will have to determine how you want to proceed from there.
Good luck.