There was a bit on I think LBC’s medical hour about nail damage saying how certain situations can lead to the nail not properly growing back and may never will. They were talking toenails, but I guess the same is true of any nail.
I’ve had a couple of nails go black and drop off. Toenails though. First grew back eventually but a good 6 months at least. Took about 3 to drop off. Second time was last August I think, dropped off in December, and still not grown back fully. Got most the way there but seems to not be growing any more and yet my other nails are and need cutting, but not the toenail.