Not sure if this counts or actually means anything, but Pokemon Ruby and Sapphire have unseen data on cry listings and index numbers. While most people know about the index number listing, and Chimecho being the last one listed, the cry data is much more interesting, and can likely give some background on when Pokemon were added into the game.
>Kecleon is the first Pokemon on the list. It was also heavily used to advertise Gen III early on, so it was likely the first Pokemon made for the gen.
>Electrike's line is the first evolutionary line listed. Otherwise, there's nothing too interesting going on with them.
>Latias was added very early on, and was also a Pokemon that was shown to have a few revisions, like the Latias/Blaziken hybrid concept art. Latios, however, is one of the last Pokemon added.
>Sharpedo was added very early into the game, was used for advertising, and was usable in early demos of the game. Carvanha, on the other hand, is added a bit later. The Sharpedo in the demo is underleveled, so Carvanha probably didn't exist at the time, and Sharpedo was just a one-stage mon.
>two unused Pokemon in between Taillow and Swellow.
>Poochyena and Mightyena are added much later, they were likely fodder mons for Magma and Aqua to use, and nothing more.
>Despite appearing everywhere in the final game, Linoone's line are some of the last Pokemon to appear.
>Chimecho is still the very last Pokemon, like it was in the index data, appearing after the event legendaries.
