I'm amazed at the number of times I've had to say these things on this forum. Here goes again:
I'm going to add some comments to your play-by-play of the charts.
- To the extent that they were reliable at all, chart numbers were a snapshot of record popularity at a given moment. Zero relevance to any other moment, including now.
And there were time when the whole chart was "thin" such as in the Christmas season when there were fewer releases and lesser sales. So a March or September chart is not the same as a December one.
- A peak position on the Hot 100 shows a given record's performance, relative to other records, on its best week. So a song that peaks at #15 is not a "Top 15 smash". It's a record that, on its best week, did less well than fourteen other records.
And when there were few good releases, either by "luck" or the season, being #15 in a weak period might be the same as #90 in a strong release period. And in those weak times, perhaps only the top 5 or 6 songs might be truly meaningful.
And here we get into what the Drake organization called "turntable hits" where there were songs people loved to hear on the radio but did not ever go out to buy.
- Albums began outselling singles in 1969 (both were on an upward trajectory at that time).
And that is what forced stations into developing "call-out" research toward the mid-70's because the old standards of singles sales and requests were no longer valid.
Further, as the multitude of FM signals jumped into the competitive environment, we started getting format fragmentation where Top 40 spawned progressive rock, AOR, Chicken Rock, AC, oldies and so on. So, if a record sold well, we did not know which format or formats it belonged on.
- Singles sales peaked in 1974, and began a rapid decline following that. It took fewer sales to reach higher positions. Album sales continued to skyrocket until the end of that decade.
And by the beginning of the 80's, we discovered Auditorium Music Tests because so many successful format included or were based on non-current music. Even CHR stations did library tests for their gold selections.
- Any attempt to assess the popularity (at the time) of records from 1974 on (at the latest) that doesn't factor in album sales is deeply flawed.
And even then, we don't really know which partisan group was buying the album.
- Top 40 radio's troubles accelerated along with the decline of singles sales. As young adults found alternatives on FM, AM Top 40 stations were increasingly female-heavy and very young----8 to 24, rather than 18-34.
And that is why the FM Top 40's that lasted for a long time starting in the later 70's had a distinct adult approach. As an example, Bill Tanner's Y-100 morning show, "Tanner in the Morning", frequently interviewed Janet Reno, the Attorney General. Not a teen magnet person for sure.
- Any attempt to assess the exposure of records via airplay that doesn't include MTV in the early-mid 80s and formats other than Top 40/CHR from 1974 on is deeply flawed.
And there were plenty of MTV and VH1 songs that were not hits, particularly ones with great videos but horrible music.
And absolutely ZERO of the above tells you anything about the popularity of a given record today, which is all that matters.
That is why, in music tests we always say, clearly, "score each song based on how much you'd like to hear that song
today."