Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
The dex entries are placed in a sprite order, you can see the sprite numbers in a couple of files in the graphics folder. See the second sheet here for the full list compiled using the Pokedex files and agbmonsp in the source folder...
I registered here just to write this post.
After months after finding this topic for the first time, I finally decided to search for clues and hints telling what Pokemon were left out of Gen One. I've always thought it must have something to do with existing new evolutions of old Kanto Pokemon...