Simple. When it is there, the channel is (H)idden in non-sub's guides. When it is not there it is shown or not hidden (in non sub's guides). It has never carried any data.
Well, it helps if one is actually a subscriber. Listing all of the descriptors at the time for all channels and watching what happens for some time helps.Thanks for sharing the tidbit.
Just curious how it was discovered, doesn't look obvious.