I can try to answer them, but others will probably answer better.
1. In season mode and play now mode, I believe roughly 6-8 teams are missing from the file, because that's how many are created in the game. In each file, it's obviously different missing teams, so pick wisely. Remember, just because there is about 24-26 teams in the roster, you can only play as 8 of them, so again pick wisely.
2. I believe WWBlue is taking on the task of changing the rosters of some teams. Ratesports are obviously a little outdated since they're from TC. Also, I believe due to the game, teams have way less players than a 53 man roster. So, on the Steelers I just have Redman and Rainey on my team.