I literally don't know what I did to break it. None of their items show up for purchase.
The shop IDs are the same. The item IDs are the same. I thought maybe it was a issue of setting Sell Price values differing from the items, but they don't seem to do anything when reverted back to vanilla. I didn't mess with the ESD ranges.
I feel like I did something very obvious and stupid, but I don't remember what it was.