Everyone already knows the best years for music were 1983 and '84.
But here's an additional piece of evidence: the Billboard year-end chart for 1985 was mainly made up of songs that had been released before 1985.
There are always some songs released (as singles or on albums) in the end of the previous year whose success will take off during the current year. But for a majority of this year's hit songs to have been mined from earlier releases? Was this year so empty? Well, if it's 1985, then yes, let's try to keep the fun spirit going from '84.
Of all 100 songs on the '85 chart, only 40 were released in that year. A clear majority, 60, were released either as singles or on albums that were released before '85. Almost all of those were from '84, but there were also 3 songs that had been mined from albums released fully two years earlier in '83 ("Neutron Dance," "All Through the Night," and "Penny Lover").
It's not just that '84 was one of the single greatest years for music, it was also the final year of the early '80s manic phase of the 15-year cultural excitement cycle. The crash / refractory / vulnerable phase began in '85, and that would begin shifting the zeitgeist away from fun-loving new wave and toward emo soft rock and power ballads.
That set up one hell of a contrast between albums released in '84 vs. '85 -- and evidently the audience was still resonating with the earlier phase and rejecting, at least for the year, the new phase. Just have a look through the albums released in '85 -- the most notable ones are from indie bands (Psychocandy), not mainstream ones. That was the start of the college rock / modern rock bubble of the second half of the '80s.
I don't know whether this is part of a more general pattern, but I'll look into it. That is, looking at each of the three phase transitions during an entire cycle, is there a tendency for one of them to be resisted more than the others?
I know I still preferred the early 2010s music to that of 2015 and after -- that's what first drew my attention to the existence of the excitement cycle in the first place, how emo everything became all of a sudden. You'd think people would be most averse to giving up a good thing, like the manic phase, to plunge into a refractory period -- not leaving behind the emo victimization phase for a return to normalcy, or leaving normalcy behind for an excitement spike.
Then again, maybe this is unique to the '84-'85 transition. In any case, something highly unusual and worth noting for the pop culture historical record.