Anderson and Roberto came back the next day with a solution. All of the 14-foot boards on the North side of the deck need to be pulled up and realigned, with a different system for measuring than we had used the day before. They measured each end of the board to ensure proper distance, anchored those points, then measured the midpoint, anchored that, and then screwed down the rest of the board with uniform gaps. Due to some minor variation in board widths (1/8 inch or so), this meant that the gaps between boards was not uniform across the deck. Despite this minor issue, it would lead to boards that were straight across the seam.
Once the 14-foot boards had been re-installed, they set to work on cutting the last boards on each edge. These had to be slightly narrower to match the exterior framing dimensions.
At the end of the day, it all worked out, and we could collectively celebrate the completion of laying down the boards for the deck.