I checked my Hot 100 stats which I made two years ago (I need to update it!).
OSD was charted in 1996 (I talk about Billboard's year). 1996 was strange year with lowest number of different songs on whole chart, in Top10, To5, Top3 and with lowest number of #1s.
Number of different songs on Hot100
Number of different songs on Hot100 in Top10, Top5 and Top3
Number of different songs at #1
I think airplay componet was huge (like streaming nowdays).
Also you can find how BB Hot 100 was changed when they started using SoundScan
