All right, I have watched, in quick succession, all of the the Hand arc shows that culminate in The Defenders. Thought they were great, but I can't help but be confused by something. How does the Hand's resurrection trick actually work?

In Daredevil Season Two it seems simple. The Hand have the secret of immortality and seem to use it liberally. None of the Ninjas seem to have heartbeats, implying they are all undead. Nobu comes back from the dead and even a low-level ninja Claire pushes out a window shows signs of being resurrected. Nobu quickly gets up after his fatal fall, by thanks to Stick being nearby waiting we discover that decapitation can end them. We don't know if the rest of the ninjas that were killed walked away. Did the ninja Claire killed resurrect again?

Iron Fist muddies all the waters. Through Harold Meachum's resurrection it is revealed to us that you only need the treatment once, but every time you come back you become more evil and irrational. Harold takes days to resurrect the first time. Bokuto, like Nobu, seems to do it in less than a minute. Harold stays dead long enough that he can be cremated the second time. 

And then in Defenders the idea that they can resurrect on their own gets muddier. Every time someone kills a finger of the Hand they make sure to cut off their head to keep them dead. Bokuto gets shot and doesn't mind. So you'd assume the instant resurrection is in play. But they also seem pretty clear that they need more ancient dragon bones not just to make new warriors but also to stay immortal themselves, and Alexandra is sick and dying permanently despite the treatment. Plus, although evil the fingers seem quite rational, so presumably past resurrections didn't have the same effect on them as Harold. Also, the dragon bone stuff is super precious and limited, which makes it weird they resurrected that low-level ninja but maybe that happened a long time ago when they had more. And the fingers have heartbeats, Daredevil listens to one during an interrogation and he'd have noticed if Madame Gao didn't have one. In Daredevil season one Nobu had a strong heartbeat, but could mask it. So are they a different form of undead than the ninjas? Than Harold? Do the ninjas all know Nobus masking trick? Because that seemed like a special ability and he didn't mask his heart the whole time. 

So, did the fingers fear what happened to Alexandra would eventually happen to them if they didn't get more treatments? Or, If I were writing in for a Marvel No-Prize I'd postulate that the fingers also need the dragon bones to avoid the irrationality Harold Meachun exhibited. Something they don't mind in their low-level resurrected but can't afford in themselves.

Maybe I'm missing something. Did it make sense to you?