Hey, another AM3 Sonic. One thing that immediate jumps out to me is Sonic's render on the first page. I wonder if Uekawa used that one drawing as reference for his concept art?
Seems like it's a pose that they reference a lot. And here's a pencil case that I also scanned. Link to scans. Seems that artwork for Sonic, Tails, and Knuckles come from that SegaSonic style guide someone here was looking for.
Some recent artwork I scanned: Sonic X magazine preview ad. Link SegaSonic notebooks. Link 1 and Link 2 Illustration on one of three Sonic Chronicles shirts that were given in contest. Link Original version: Other version with his right colors I made:
I did some color correction on the artwork to bring it more in line with the colors used on Adventure's artwork (because why not?)