Well, they've known the "KDKA" call letters for as long as they've been alive and in town and paying attention to stuff like that.
Someone who's 35 and just starting to care about local TV newscasts doesn't have that connection. Nor does someone who just moved to Pittsburgh.
Yes, via research. And what they found was something that we kinda knew already---they knew what network they wanted and maybe a channel number (though "What channel is (network) on here?" is one of the most common questions known to man).
It's been going on for 30 years. The video quality is atrocious, but it's the only copy online---KNBC Los Angeles in 1995, becoming "NBC4", with weatherman Fritz Coleman (left) and sports anchor Fred Roggin (right):
And now, with a kazillion channels, channel numbers are less important---but "NBC Los Angeles" (which is what KNBC identifies as now, with a "4" on the screen) tells a viewer what he/she/they needs to know and most modern TVs and remotes, with voice function, will get you to the right channel on that voice prompt alone...no channel number needed.