As for Rayquaza, the early design seems to suggest that at one point, it had fewer, larger lines with only one loop per thin segment, only two fins per thick segment, and a line separating the head from the neck, as if the head was meant to be another segment like those running down the body.

Aww man, my browser mangled the image. Lemme try that again.

So, as I planned to elaborate, it seems like Groudon's final backsprite might reflect an earlier design. The lines on the forearms aren't a perfect M on the final, and instead seem like they modified the cross-shape of the original.

Here we are. Had to fix a pixel error on Groudon's sprite; probably the result of a botched cut+paste by the person who used the pad. Groudon's sprite resembles the prototype design that's been floating around for a while.

A bit late to this, but whilst doing some digging of my own, I found that your diagram features the finalized Groudon and Rayquaza designs, but their scratchpads feature slightly older designs as well. I'm about to hit the hay, but I can post them when I wake up. Groudon's matches prototype art.

I play a Sapphire half-dragon in a campaign currently going, so when you announced you had made the new official art for the gem dragons, I have been waiting all week to see your rendition of the sapphire all week.

The monster manual dragons have different art showing off the differences between the different growth stages. Will that be the same with your gem dragons?