Mixture of both, all sides would regularly pull their units out of the line to re-equip, reorganize, and retrain after heavy combat . Alot of times if a new unit was being formed they'd pull some of the veterans to form the core Cadre and leadership of the new one. Most that were recovering from wounds would be placed in new units after they were healed as replacements or cycled as instructors for training centers so their experience wasn't wasted.