Can't complete Oklahoma Challenge?

The challenge says ''Recruit 10 Comancheros, Guachos, Morochucos or Vaqueros in a single Skirmish/Multiplayer game.

I've done that twice (got 10 Comancheros from the Tavern/Native Embassy).

What am I doing wrong?

Edit: Nevermind, I somehow did it. The first two times I tried normal games. The 3rd time I did a deathmatch and it worked for some reason.