I'm so sorry I hadnt read this thread previously, I read your first post in the beginning and didnt have anything to offer as it was teeth related - it now screams NTs all the way through to me

So many hugs. These really are the hardest things to deal with. They got harder for us as DS reached about 2.5 too as the nap dropping was just awful and his NTs became more vocal and angry
As I said in my PM, OT is the cause for us - every. single. time. This age is not a good one for me as far as routine is concerned but if you can get him better rested it will help. Of course the teeth and developmental changes will just be adding to it all.
The general advice is to not to try to wake them during a NT but to be honest sometimes we are able to wake him and it does actually help - this is not what's recommended but does help us. There are times when he'll have several NTs in an evening, with just a short space between each one, he's just not settling at all, and it's not until we actually wake him that the cycle is broken and he is able to settle to sleep soundly. I generally only try waking him if this sort of situation is happening, or of a single NT just seems never-ending.
There really isn't a lot you can do to help whilst they are in the throws of a NT. I usually find, like you have, that holding him etc just doesn't help. I just make sure I am there to ensure he doesn't hurt himself with the thrashing around and to try to reassure him.
All you can do is try to prevent them happening in the first place. The child being too hot is definitely a trigger too. Try to ensure his room is cool and he hasnt got too many layers on. Otherwise, preventing OT is the only answer really.
Wake to sleep was suggested to me too, and I do think this is a good idea. DS was older when this was suggested and at that time the timings of the NTs were not so predictable so it was hard to know when to do it, but on the few occassions that I have I really think it helps. At your DS's age I found I could predict exactly when he would have a NT (the first one of the night, at least) as it was usually 2 sleep cycles (90 mins) into sleep - do you find the same? So I think W2S would have been more succesful and I would know exactly when to do it.
I know it probably doesnt help, but just remember that LO's know nothing of a NT. It is awful for the parents to see but a LO wont remember it.
Lots of support from me. Its so tough

DS has gone 3 weeks or so without a NT after months and months of them (with this 1-0 nonsense), and they've started creeping back in over the last few nights

Think it's down to him not being too well with a cold.
Massive hugs xxx