There are duplicate channels. For example, if you enter "3" on the remote, Contour will go to channel 3, which is HD. If you press "1003," Contour will go to the same HD channel, albeit channel 1003. It's the same channel and program.
I think the secret is in the Guide button. If you press the Guide button twice, you'll get view options. If you choose "All Channels," you'll get a sequential list of all SD and HD channels to include...from my example...channels 3 and 1003. If a channel is only SD, you'll see this SD channel in the list.
There are other options to view only HD Channels, My Favorite Channels, Free to Me, etc.