Many discussions begin with a comment on a station that has gone up or down in the public-release Nielsen data.
This information is part of highly detailed reports that allow advertisers to view the ratings data by age group, gender, ethnicity, geography, education and income. That precision data is copyright and not released to the public. Stations pay for it to show to advertisers.
Because we love lists. Top songs, top teams, top hitters, top passers, the ratings company releases an overview. It is intended to promote radio and the ratings company without giving away anything of value. Advertisers pay to reach people in very specific age groups, and will often specify criteria like "men 25-44" or "Hispanic women 18-49" when they get quotes from stations (or do automated buys). They don't use the 12+ numbers.
So when looking at ratings, consider whether the station has done better or worse in its target demographic. That is all that matters to the programmers and sales staff of the station.
Two real world examples are WFAN and WDUV. WFAN has spent the better part of three decades at the top or near there in revenue in the New York market, but it is generally somewhere around 15th (give or take) in 12+. Yet it delivers adult males very efficiently and does very well. WDUV has lead the Tampa market for well over a decade at #1 in 12+. But until it made recent music changes, it was about 15th in revenue; that's because in the sales ages, generally over 19 and below 55, they were about 15th and got very limited revenue.