Continuing our discussion from the Seven Sages thread.
I find it highly unlikely that they planned Gen 5 tag in from Gen 3. Most of it is on the fly. I mean Generation two was actually a Sequel to the Pokemon games. They basically make it up as they go.
The Japanese copies of R/S/E say that Bill and Lanette created the PC system together, have them listed as co-designers/developers. And both were fairly new in the games' story wise.
Other small facts. Hoenn was the origin of the Battle Frontier as Scott creates it. It is later brought to Sinnoh which happens a few years afterwards.
Bulbapedia has a small history based on key points of interests in the games. Exact dates are obviously not accurate but general theme Gen 1 happens at the same time as Gen 3.
http://bulbapedia.bulbagarden.net/wi...porary_history