Arbitron-rated markets are now calculated differently, while unrated markets are based on signal overlap to calculate the number of stations in the market, and due to transmitter site differences, it is possible for different group owners to have different limits in the same market.
In our unrated market, my market definition is 15+ stations, while for my local competitor the number is 14. So I can have 4 FMs, which I have, but my competitor can only own 3.