Sorry about the misunderstanding nippjas, I completely agree with you, it does use part of the PSIP data set. I was really just referring to the guide info which they get from a provider. Absolutely, you are right, they use the PSIP data to grab the call letters, and the channel assignment mapping. They use that data to associate the channel as an index into the programming guide.
Unfortunately, with the 921, they are just re-mapping the analog program guide onto the digital channels. No sub-channel data. The analog doesn't always match the digital broadcast either. They could have done this hack back in January, well before they added the infrastructure the 811 uses to do it right. It just amazes me that it took them a year to do such a half baked fix which would take all of an afternoon worth of programming.