As the disclaimer that was used on pre-2005 countdowns on WCBS-FM used to say (paraphrasing): "The information used for this countdown was compiled from various sources and is consistent with our format". Actually meaning as you say: compiled from WABC, WMCA, WHTZ "Z100" playlists, possibly others (WOR-FM, WXLO "99X", WWDJ "97 DJ", WNBC, 97 WYNY - I don't recall them ever using a WINS list). On the earliest editions of the Top 20 Countdowns with Norm N. Nite that began around 1982 (first as a Top 5 mini-feature, expanding to the Top 20 two hour show shortly thereafter), the national Billboard Hot 100 Chart would be used, but like the current show the exact source wouldn't be mentioned. Several years ago WCBS-FM decided to "rename" the show the "New York Top 20 Countdown", emphasizing the New York area playlists, which have become available through a few websites such as
http://www.musicradio77.com/surveys.html,
http://www.musicradio77.com/wmca/surveys.html and
http://las-solanas.com/arsa/surveys.php. Thus began the use of the disclaimer above for awhile; not used since about 2003-04, about the time when the 2 Saturday/Sunday Top 20 Countdowns were briefly discontinued & later brought back as a Sunday 7PM 1 hour "New York Top 10 Countdown" show.