Reading your response, the question that comes immediately to my mind is how good was the methodology and how trustworthy were the numbers coming from the methodology used for that sales research. I mean, back in the 1950s, we didn't have today's sophisticated research techniques nor as much knowledge of statistics so it seems, to me at least, that any numbers from that era could be considered suspect by today's standards.
That 50's, 60's and earlier 70's music "research" was done directly by stations themselves. It was not done by trained researchers at professional research companies.
Each station had its own "system". I ran several Top 40 station in that era and here is what we did:
First, we had an "intern" (go-fer) call a variety of record stores and ask what songs were moving. This was informal, and we often found record store employees who had been rewarded by record promotors to report songs. So we rotated the stores and tried to use independent stores and not big store record departments.
Second, where available, we got jukebox play data. That was better than the sales data, as the jukebox operators tabulated plays to make sure they loaded the boxes with money-making songs.
But in both cases, we did not get data on age and gender of the record users or buyers.
We also tabulated requests, although we did not play requests. This was helpful in detecting "breaking" new songs.
Every week, we met and looked at the data we had and then talked about our own feel about the songs. Often we had our "in demo" receptionist and sales secretary participate to get reactions, too.
After all of that, we considered things like how many songs of each subcategory, like slower ballads or rhythmic dance ones, we had on the list and in what rotations. We tried to keep the tone of the station consistent.
Like today, this is part research and part a programmer's feel for songs and for the station and for "fit" between them. The numbers are not "suspect" as the only reason to do any kind of audience-reaction based music research is to find out what to play to attract and keep listeners.