One hit spear build? (HZD)

I just got one speeding through the remaster to get to a realism NG+UH playthrough, and I got to thinking;

Does the Spear base damage increase from "In her mothers footsteps" stacks?

if so, how may playthroughs till that mission would it take for your spear to one-shot a thunderjaw?

with how early that mission is in the game, I wouldn't think it would take forever. especially if you acquire the super strong bows once and carry them over each NG+.