Well, it's not the armor nerf; I was able to experiment with some rings after posting this and it looks like I just lost almost 3k armor for no apparent reason. Either that or I've been misreading my armor all these weeks.
What baffled me more is/was the hit rating. It's back to normal today but I had just gemmed and enchanted some dps gear to get close to cap (would have taken me to 240) and last night I was at 292. Now I'm back down to 240. Perhaps I had some raid buffs that were kicking me up (though I'm pretty sure I checked after the raid split up) but I have no idea how that happened. And, unlike armor which I had a basic rounded total of 27k in my mind, I've tracked ever since dinging 80.