@EatYerGreens

I think if you retrain an upgraded unit at a province without the same upgrade opportunities they still have the same weapons and Armour upgrades as the original guys. I guess the survivors salvage the weapons and armour after the battle (even if they lost xD). I'm not sure though. That's why I always make sure I reinforce these units with un-upgraded units, hey it's war, nothings meant to be fair.