And, as mentioned so frequently (and accurately) that both cume and rating in the 6+ or 12+ configuration, literally, means absolutely nothing except in a total market "beauty contest." It is impossible to extrapolate demo, TSL, cume and ratings from that demo spread.
Even more so with PPM, based on "hearing" not "listening." If your "meter" picks up mom's mini-van filled with six people, you all "heard" the station mom is listening too, and your meter says you "heard" it, too -- while everyone else also was exposed to it, but only is part of that unknown "estimate" of what the audience composition truly is.
On the other hand, diary recall, though the standard for four decades, isn't much better, as it is a "guessing game" of what and when people actually listened, especially when trying to compile from "recall" the week prior to the end of the particular weekly sample, when so many diaries are filled out at the last second -- not ongoing, as they should be.
It's all about "science" or "fuzzy logic" -- depending on what side of the fence you're on.