Maybe I minimized the songs that were "bubbling under" the WABC top 14. It might be 10 or more. But they didn't rotate anywhere near as fast as the top 14. The WABC tribute website has access to all the weekly playlists. I think the cut off point on the chart was #14 because WABC didn't want to play a former hit song that had fallen beyond that point.
In the 60's I used WABC as sort of a model for my own larger market Top 40 station. I monitored the playlist and on a number of occasions did actual rotation tallies over more than one day.
Like most of us, we divided our playlist into a number of levels. If we truly did have 40 currents, we had at least 4 or 5 categories, ranging from WABC's #1 song every 90 minutes to new adds coming in at, perhaps, every 3 hours or so. The concept was very much like gears in a watch, where the different categories always produced different "sets" or sequences of songs.
How far back did WABC go for it's "gold" file? Maybe I should have said "recent" instead of "recurrent". I don't think gold songs went back more than five years or so. It's not like some of today's Top 40 stations that will go back to the early 2000s. Playing gold was so infrequent that when WABC played gold it had jingles announcing it.
When WABC got into Top 40, there was no rock music that was older than 5 years (they began in late 1960) so, even were they to have added gold, it would have been very recent.
Generally, stations in the rock format (remember, we called CHR or Top 40 "rock" in the earlier years) did not start adding gold until the mid-60's years. The concept of recurrents was not understood, and most of us "rested" songs when the dropped out of the Top 40.
At least that's how I remember it from my own listening as a kid and hearing airchecks from that era.
You'd have to listen to many days of music to get the rotations correctly.
For example, some stations had a "start point" each morning before AM drive, so that they had different sets in every hour. Others shuffled categories. Some of us even mixed the mid and low range songs every few days.
40 songs with a single category would repeat every two hours to 3 hours, depending on commercial loads and talk and news and other non-music quotas. With the biggest songs running less than every two hours, the lesser ones might run in a 3 to 4 hour rotation.
I "remember it" since I was a Top 40 PD in the 60's and 70's.