What's so hard to believe about 99 Pokemon? They've already advertised it as "over 50" new Pokemon. 99 is almost double that amount. That's basically 100, which is how much we got from Kanto to Johto.
They said "over 700 Pokemon," which we logically concluded means that there are at least 52. Saying "over 50" would imply less than 100, and there's nothing to suggest either way.
This more than anything. We have never seen less than 100 new pokemon. I personally hope for more variety and not just a bunch of prevos and new evos. Though I think getting 120 new pokemon would be lucky. I figure probably around 110 I would be happy. But because of all the signs of older pokemon being in this probably means this is very likely