Chances are your general picked up some retinue in the first case. Victories will always increase your good commander points by 1 (which gives +1 command per level) and there is a small chance (20%) of gaining various retinue members. The first level of command is only 1 victory, next one is after another 3 victories I think, then after 5 and so on.

In the second pair battles you probably were high enough in commander points so that you didnt reach the next level with the 2 victories.