After winning, I like to back up a couple turns and try a comeback with the other side.
I've noticed that it doesn't seem like the AI is buying replacements for any units. The F2 replacement pop-up is way in the red, and a lot of brigades are missing elements.
I thought perhaps it was because I was playing with automated replacements off, but I just tried it again in a game set to 15% replacements, and again the AI had nothing.
This seems broken. And a cheap way to win- I'll end up in battles facing regiments that are almost wiped out, so its really easy to wipe out regiments and get big NM boosts in battles that should be closer.
I believe the AI is buying each turn replacement, but at a rate that is not appropriate with its losses, and so you see these replacements always depleted, but something is happening! The AI budget is split in chunks, and one will go to replacement (with highest priority, but not enough obviously) and the rest is used for new units.
Perhaps your game pace was very high and the AI can't cope with the attrition speed. Now historically, most regiments never had replacements and new ones were formed instead.