I think all of the first 251 pokemon were created by the time the original red and blue came out. Why? It could just be a coincidence, but if you take a pokemon above level 100 up with rare candies, it goes to 250, then back to 0. How many integers are there? 0-250, there's 251(I did this trick myself, it's proven). It might be a coincidence, but considering how we already know some 2nd gen pokemon were created in the first gen, it's possible.
FC: 5043 1366 9389
I claimed Deoxys, and serebiiforums is my homepage. Good luck claiming it.