I couldn't read through all of the posts, but have you tried Feliway or Comfort Zone with Feliway? My rescue cat was a biter sometimes. Fortunately for me one of her front fangs had been extracted before I adopted her, so she never broke my skin when biting. I had bought Comfort Zone with Feliway spray to spray her carrier & my car to help reduce her anxiety when I first brought her home. It seemed to really have an effect on her, so I got a plug-in for my apartment for her. It seemed to really work! I sprayed daily for a few weeks until I figured the plug-in started having an effect. It can take a month. Once every 3 weeks like clockwork, she'd come to lie on my bed and roll around, then bite me. I'd check the plug-in and sure enough it needed to be changed. I'd change it and presto, the biting stopped. Almost a year later now and I may no longer need to buy plug-ins. You can get them for a good price on Amazon.
Also, whenever she bites, I freeze quietly, wait for her to let go, slowly withdraw my hand and don't react. She'd calm down since she was tense and waiting to see if I'd react to her biting. I didn't so then everything was fine. Sometimes after withdrawing my hand, I'd fake cry and that also seemed to work well. She seemed to feel badly and come try to make it up to me. Nowadays, she doesn't bite. Knock on wood. She hasn't bitten me in a long while, I think.
Also, whenever she bites, I freeze quietly, wait for her to let go, slowly withdraw my hand and don't react. She'd calm down since she was tense and waiting to see if I'd react to her biting. I didn't so then everything was fine. Sometimes after withdrawing my hand, I'd fake cry and that also seemed to work well. She seemed to feel badly and come try to make it up to me. Nowadays, she doesn't bite. Knock on wood. She hasn't bitten me in a long while, I think.