The damage will move slowly upwards I believe, but sometimes a new nail grows on the bottom...
I remember my snow boots totally screwed up my toe and it left a big bruise, and most of the nail turned purple.
That was a blood clot though obviously, and I guess most of the nail died. It slowly moved up after 2 months so that it was halfway up (half my toenail was non purple) by then it was like a dark black or whatever.
I then noticed that a new nail was growing. I basically ripped off the whole top layer (allt eh purple was underneath) and underneath was a fresh (thin) new nail that was growing. I wrapped my toe up and gave it a little extra protection, but within a month it all grew back.
I think you have some dead nail there OP.... but iono.
Happened when I cut my finger with a knife. Half my nail was cut but I thought it would heal. Instead after 2 weeks I ripped a chunk of the nail off because I found a thin layer growing underneath.