Isn't it logical that all of them ought to come in the same?

I went to the website for WLIW Channel 21 in NY and it had an interesting bit of information. Channels 2, 7, 11, PBS and 21 are all broadcasting from the Empire State Building. I get all of them perfectly except for 21.

They also mentioned the "double scan" which was mentioned on this site and I did but that still doesn't allow me to receive the channel.

I know that it's relatively unimportant considering the serious difficulties that some people are experiencing but it doesn't seem logical to me now that I know that they are all being transmitted from one location.