More on Nebraska PBS channels

According to _OnSat_ and also the program guide in 4DTV, Nebraska's
NET PBS channels are now to be found at T8 [T4] 600, 601, and 602. But
all I get is a black screen whenever I go to those sites. Once
recently, however, one of the channels was showing a horse race! Has
there been any official word as to why these channels cannot be found
in this place? If not here, then where? Thanks for any help --E.A.C.