Apart from 1955, which "rock era" year was MOST different from the year before it

Influenced by thisOdd years vs even years (in terms of which produce better music) thread maybe, but pulling it in a somewhat different direction.

Most music years are roughly like the year before it. Yes, there are new trends appearing, but it usually happens slowly, building over time.

I guess my candidates would be the following

1963/64 (depending on UK/US): Merseybeat/"British Invasion" changing the charts in a lot of ways. May actually the the answer here

1977: Punk/new wave making an actual impact ("Anarchy In The UK" and the first Damned single were in 1976, but they were hardly notable then)

1991: "Alternative"/grunge turning the charts at least partly upside down compared to the couple of years just before. Suddenly what was considered "underground" for years and years suddenly became mainstream.