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.