Hmmmmmm, maybe an interesting, but good, speculation there. Someone may not even know of a pattern change, unless a FS measurement is taken, or the FCC contacts the station to say, "We've noticed that you are out of compliance from a couple of monitoring stations." I don't remember what AM station it was, but in the 80's a station was contacted by the FCC for being noticed a few Hertz off FREQ measured at night. It's been a month that I've noticed that slightly off-FREQ station on WTAM's 1100kHz now. We'll see just how long that's in there. They are my fall-back for C2C AM on my drive home, when the local 1240kHz station, (Yeah... A Graveyard FREQ.), goes off-air, or just dead-air. That happens a lot, and their newer FM translator doesn't help when there's no audio to that either.