I have this veteran survivor with melee, cutting and bashing around 10, but 0 piercing (almost a game year of whacking stuff with a nodachi). I gave him a rapier, but despite killing hordes of zombies, his piercing skill would stay at 0. He also wouldn’t block, despite rapier having WBLOCK_2, nor would get his weapon stuck even once.
So I tried a pointy stick, because spears have better training ratios (always train piercing first). Piercing stayed at 0, despite every hit being described as “You pierce x”. Unlike when using the rapier, he wouldn’t use any techniques when using the spear (with the rapier literally every hit was rapid or precise).
I checked the savefile - piercing was listed as never trained (lasttrained: 4800, like barter and swimming).
I tried replicating it in debug mode both with similarly inflated skills and 0 in all - neither rapier nor pointy stick did anything to piercing skill. Only steel spear worked. I thought it might be focus, but the effect was the same with focus around 20 and 90. I got my debug survivor high on meth and then made him break a pointy stick over a zombie hulk - melee skill went from 1 to 2, bashing from 1 to 2, piercing stayed at 6% from 0 to 1.
It was all in build 900f26d, version 0.A-2119.
I also found an unrelated minor issue: when using “set all skills” debug command, practice doesn’t get rescaled properly and can go from like 10 (30%) to 0 (200%).
tl;dr Rapier and pointy stick don’t train piercing.