A unit without DCC always has to retreat after combat. A CRT mandated retreat becomes an additional loss. If the CRT calls for losses, the losses are increased by 1. There is a neat feature of combat. This allows up to double the maximum losses of a normal combat.
Most regiments have three steps.
When the final step is lost a strong- point can be formed. The strong point is weak and immobile, but still must be destroyed. A unit can take reinforcements provided it still has at least on step left. You cannot give a reinforcement to a strongpoint to bring the dead regiment back. Stacking is three high.