: is this where the puzzle joint is located

If you are talking about what I call the Four Corners, no. The flat spot is on the top of the hull side panel, and it has been nicely reduced through a combination of sanding to rebevel slightly and tight stitching. There is still a short flat spot where the deck edge has bit of overhang, but I'm just going to trim it.

BTW, I had the same problem you did with the puzzle joints. I planed off some of the wood because, when wiring together the deck pieces, those joints did not come together with any semblance of smoothness. I ended up with a small gap in both of them which I filled with dookie schmutz and will have to sand down. I don't like the fact that there's no solid wood in those spots, but the whole thing will be sandwiched between glass layers, some of which are overlapping 9 oz tape, so I doubt it'll break.