I was just asking the same question after having caught up with 12 seasons on Netflix and saw that on xfinity stream app I just downloaded that does not have episodes 1-11 there, but has 12-14.
I see no one has answered your question here. Terrific.
It's normal for only the past 2-4 episodes of a current season to be available. Older episodes expire and may eventually appear under the rental/buy model. This isn't a Comcast issue, but mainly limitations imposed by the media companies and is common in the industry.
Criminal Minds is on CBS where I'm from and I don't know if it's the same everywhere. But I know CBS has their own streaming service so I wonder if that is the reason why. CBS charges for their streaming service as well, so why give for free when they can make a profit, I'm thinking they are thinking. I only have episode 15 on mine currently and thats just annoying as heck that I can't catch up on the season from my cable provider. Unless.... CBS doesn't charge customers that have certain cable providers. I think I need to check into that one.
I am having the same issue with blacklist. First few episodes of the new season are only available if we pay for them. We just finished watching the other episodes on Netflix and we were hoping to watch the new season on on-demand.