[Imp]

As georgesedlak said if there are survivors they can quickly get the unit up to speed.
If its wiped out then it buys a new unit at that countrys setting losing any experience gain.

Common practice to spread "Veterans" among the new recruits to get them up to speed.

Its also common to try & identify them & kill them making the rest an easy target ask the Americans in Vietnam.

Generalising its only after that time period that training makes the whole squad a combat force before that maybe 2 or 3 men tops would be the backbone of the squad, get them & its game over.
This probably applies to most 3rd world countries even now & is reflected in the experince factor they are given in the game.
Most of the main players took on board British, Israeli training methods to help aleviate this problem & while I have not checked thats probably reflected in the game to by them leading the experience tables.

A lot of work has gone into this game & to me it shows despite the fact some things are abstracted it plays in a way that feels right.