The 55+ does not matter, as agencies don't look at them.
Look at how a station does in 25-54 (or, generally, 18-49 for ethnic stations) and you will see how they bill.
There are formats that under-bill their rank, such as Alternative Rock in most markets. Ethnic formats, particularly Spanish, may not bill in proportion to their rank.
But in general, agencies don't first think of the format... they think of the rate offered and the Cost Per Point that the offer yields. Sure, an agency may not want to buy two AC stations due to duplication, but much of the rest of the deal is about delivery and cost.
This is why, with rare exceptions, I never look (and never looked) at 12+. I look at the target audience, and don't pay much attention outside that focus area.
All most of us see is 6+. It would be nice to see the demos again. I saw both Cincinnati and Louisville Arbitron's back in the mid 1990's. There was a big difference in both markets depending on which side of the Ohio River a "average" person lived on.