I noticed today when trying to find a particular channel on the grid guide on my Nvidia Shield that I couldn't find it. And after some research, it turns out more than a few channels are missing from the grid guide even when "All" is selected.
From the screen shots below, you can see how many channels are missing from the onscreen guide:
The web page guide has some of the missing channels, but is missing others:
There are probably many others, but it's hard to compare the entire guides.
The on screen guide from the Shield also shows "National Geo HD" which is a DRM channel and should not even show.
It seems the grid guide is totally hosed between the different platforms.
Nvidia Shield on screen:
Channels web page guide:
HDHomerun Source channel config: