It would take Dish to actually call each and every network, go over each and every show, and IF they actually got the right answer, then know if a listing is correct. By the way, that would have to be after it is in the guide because changes are made sometimes a day or two before airing. Not on the big networks, but often on Bravo and others. Also, why is it assumed the information given to the guide provider is correct? No doubt the provider makes some mistakes, but how often is it not their fault?
If changing providers is an answer, and it would improve, I don't know that for a fact but is possible. But to suggest Dish (Or Direct etc....) can actually contact, every week or so every network about every show is not being realistic even that they will get the correct answer.
I know one first hand account of this. I was in the Regis and Kelly audience for an advance taping. I was told when it would air, and it showed when they said it would. Showed in the guide that is, but it was a different show that actually aired, because (as I found out after writing them) the guest of the show that aired had become popular in the news (Anderson Cooper) so they wanted it to air. That's just one example of why the guide may be out of the control of Dish for sure, and sometimes even the guide provider. I have seen this with reruns of David Letterman also where coincidentally the show in the guide is not shown, but a show with a now popular guest or one in the news is.