More confident that my process worked, I planned a more ambitious piece. From the Facebook post on the day I completed the piece: "93,450 stitches in 402 days. A little over 232 stitches per day average. With 18 stitches per inch, that means each day I covered the area of a quarter. The last two colors had 16 stitches each."
8/28/2018 note: I notice that I stitched reference marks around the perimeter. I no longer do that. (With the exception of StarStitch SIRDS.)