The move was at WCBS-FM to "Jack" was neither completely smart nor sound. Had format options been researched properly in the first place, WCBS-FM would've remained a personality oriented station with an updated playlist to better calibrate song age with desired demos.
I completely agree it was necessary to evolve CBS-FM's programming, but "Jack" was not the right solution.
Jack was working much better than the "old" CBS-FM oldies format. Jack was starting to be much more significant in 25-54.
As I said before, the NYC format was changed not because Jack did poorly but because CBS corporate became aware of (and frightened by) the rise of their own FM in Philly which moved from oldies to what we call classic hits today. No, not a full 100% move, but a very definite increase in sales demos.
There was a group of the more ratings-knowledgable radio people and folks from ad agencies and Nielsen (when PPM was still a joint project) who were members of a committee that attended meetings and got the PPM data from around 2002 onward from Philly and, later, Houston before the PPM went live.
I was invited to join that group and I saw what was happening in the PPM. While not all stations encoded, the changes in WCAU-FM were obvious and we could see the change as they sort of created a 70's core classic hits format 20 years ago. While the CBS folks did not comment, all of us knew when they went to classic hits in NYC it was because they did not want anyone else to get that format before they did, particularly since they owned a positive image.
Were the PPM test in Atlanta or Denver, that scenario would not have happened. But Arbitron and Nielsen wanted a test that was a relatively fast drive or train ride from their Columbia or NYC headquarters, and Philly it was.
Before going to Jack, the CBS-FM folks did not envision either how PPM would work or how their format might evolve. It was not until the Philly tests showed that the PPM was going to work and how it would affect some formats more than others that they made a strategic decision to anticipate the PPM with a format that would win in that new ratings service.