Here’s a repair! I guess someone felt that a shim was needed under the board. I’m not even sure what the fix was supposed to be fixing. From this view, outside, I couldn’t see what I was looking at. Removing the board, I found a spruce shim of sorts.
I still don’t know what the mess on the edges was or was supposed to look like, but it sort of resembled a strip of purfling made with black layers of unbelievably filthy glue on either side of the spruce core. It’s all gone now!