My point was that top40 (“most broadcast” + “most purchased”), and Spotify’s “most played” (i.e. “most listened to”) are distinct concepts. For the past, we only have access to the former, not the latter, because nobody can know exactly what songs people were listening to the most (e.g. which records/wax cylinders were purchased and then played more times in total; or, even further back, which pieces of chamber music were performed more times; or, even further back, which folk songs or hymns were sung more, rather than transcribed more.)

To focus on only the recent past: we only know about radio plays (determined by cronyist industry dealings) and about record/8track/cassette/CD/iTunes sales (where a record sale could represent a purchase due to virality—i.e. a purchase for status-signalling/watercooler-conversation/joining-a-subculture reasons, but where nobody actually listens to their purchase more than a few times; or it could represent a song everyone loves and puts on repeat all day every day. And a purchase could represent a fad that fizzles out; or a classic in the making.)

We can talk about what the top40 billboard charts were doing back then, but what people were “most listening to” is very likely a wholly different list with little intersection to the billboard chart. Just like this Spotify most-played list is actually an almost-entirely-distinct list from the current radio top40!

Intrigued that you mentioned the 1940s. Glenn Miller?

And all the other stuff that was going on in Jazz in the 30's and 40's