So, the French doors (south, center) have begun to move apart from one anther. I think it's actually the west side of the house is settling a touch faster than the east, and thus the frame is widening a bit. Why this matters is the catch between the doors doesn't always 'catch', and the door stays open.
So, even though I spent a bunch of time beveling (is that the right word?) the hinges into the frame back when I put them on, I realize the easiest solution is to move the west door slightly to the east. Here's what it looks like at the hinges before I started:
And after I put in a little shim behind the hinges, all worked well: