Some not-so-deep thoughts:
Arbitron/Nielsen identifies something like 80 specific format identifications, something for everybody... well, not quite. Most of us can find a mix of what we like, until we hear something we don't like, or more often than we want. The term "Adult Contemporary" can apply to a number of variations. KXXO has always identified itself as "Soft Rock", which I personally find disingenuous. Its actual music mix has tended to be close to our Sunny 102.1 format.
Most successful music format stations work with a play list more complex than just "200 songs". When playing familiar music, there is a risk is that someone might hear a song too often. Vertical and horizontal scheduling, along with different rotation frequency, provides the average listener a feeling of variety and familiarity. The rotation patterns are based on the listening habits of the average person. If you listen to any music station longer than the expectation, you'll start noticing that "short play list".
AC stations typically don't play "new" music, waiting until it's an established familiar song. The mix of current, recurrent, and older established hits will vary depending on the station, but one constant with any music station will be that newer music will be regularly added, while older music will always be dropping off the play list. Every successful station evolves; if you're selling to a specific age group, you must accept the reality that you will be losing listeners leaving that age group, and gaining listeners entering your demos, every day, every week...
On another serious note, what are the odds-makers saying about the 2016 KRWM Christmas Music start date?