The 0 slot vs 1 slot difference is probably a distinction made for balance rather than realism.
I would figure that something like a Falchion would take up more weight/length than either, but it's 0 slots as well.
Cut/Pierce/Blunt also seems to be a distinction made for balance rather than realism.
Against anything below mail it might make sense to count some of the spiked mace's damage as pierce, but the same applies for iberian mace, warhammer, the polearm maces, and the 2h mace that's just called "Mace". However, it would still make sense that most of the damage would come from blunt force trauma, since the spikes are tiny.
Similarly, against tougher armors, it'd be sensible to treat almost every melee weapon that isn't pick-like or a pointy tapered thrust as doing mostly "blunt" damage for most hits based on some factor of weight vs. how likely the weapon's shape would cause it to bounce off, but obviously this isn't the case.
Every decently heavy weapon should be able to knockdown as well if you go by realism, but again, that's not the case.
Heck, the warband engine doesn't even allow non-blunt weapons to knockdown by default, even if they have the knockdown flag. Doesn't work for any sort of ranged either, you have to make custom scripts for both.
