NPC spawns are random, and their move set increases as you level up. This is particularly true for the sword moves, as the low level marked ones will not use any, but as you increase in level they'll suddenly start with a sword in hand or pick up weapons on the ground, including your own.

So, sadly, it boils down to "block the NPC a couple of times and see if there's something you don't have yet".

Some moves are specific to rare spawns (like the guy in underpants with only the slap move, or the khalt sword techniques unique to the heavily armored khalt NPCs that sometimes spawn.