November 1, 2001
- Has an early frontsprite and backsprite, with a mostly finished design.
- Its name (チリーン Chirean) has already been finalised.
- Currently dex number 318 and index number 341.
February 14, 2002
- Has a dex entry, still dex number 318.
March 2002
- Receives early concept art that’s mostly the same as its release art.
March 25-31, 2002
- Has the same early frontsprite and backsprite from November 1, 2001.
- Normal type at this stage of development.
April 20, 2002
- Not in a list of Pokemon present at that point of development.
May 2, 2002
- Has new dex entries, one for each version.
- Still dex number 318.
May 14, 2002
- Not in a list of Pokemon present at that point of development.
July 17, 2002
- Now located at index no. 411 (same as final), doesn’t have any stats yet.
November 21, 2002
- Ruby and Sapphire release in Japan.
- Final dex number is 358.
December 26, 2002
- Receives final concept art.
July 8, 2004
- Anime debut in Japan.
Interestingly, a file was found that details Pokedex evaluation messages, and it has a commented out remark that there would be 28 old Pokemon and 134 new Pokemon obtainable, when the final game would actually introduce 135 new Pokemon.
This matches with the lists of Pokemon from April 20, 2002 and May 14, 2002, which both describe 28 old Pokemon and 134 new Pokemon (a number of which don’t have confirmed names or concepts yet).
Chimecho, anything resembling it, or even a placeholder for it is completely absent from both of these lists.
Chimecho was present in the game at index no. 318 up until being removed sometime between April 1, 2002 and April 20, 2002.
Despite no longer being in the game, it would obtain two new dex entries by May 2.
It remained absent until it was put back into the game at index no. 411 (after every other Pokemon already present) by July 17, 2002.
Torkoal’s scrapped pre-evolution hadn’t been fully replaced by Nosepass at this point, but apart from that, Chimecho being readded appears to have been the last change made to what Pokemon would be in the game.