Mid 1986-early 1988 - All should have had much more substantial late 80s culture at the forefront of pop culture, rather than ambiguous mix of core/mid/late where trends from 1983-85 are still everywhere.
1990 - First half should had much less core 80s influences being acceptable considering they co-existed with incoming 90s culture that was clearly more in style and newer all throughout mid 1989-mid 1990.
1993-1994 - Early 90s culture should have been much less compared to mid.
1996 - Mid 90s should have universally ended in the early to mid 1996 rather than early 1997 - this is largely due to slow adoption of UK and Japanese trends including tech catching on.
1998 - The core/main Y2K era should have 100 percent universally started in spring 1998 rather than late 98 this is largely due to slow adoption of UK and Japanese trends including tech and other factors.
2000 - Should have been more techy than it was
2004 - Should have been mid 2000s the entire way through
2005-2006 - Should have been more late 2000s even though it already kinda was
2007 - Should have had more had more 2008 like tech and pop culture changes - nothing happened
Late 2007 to mid 2009 - Should have had more proto 2010s aspects and less core 2000s.
Late 2009 - Should have been fully 2010s
2010 - There should have been more tech changes and core 2010s asthetics should have had more exposure
2015 - Should have been the official start of the late 2010s, from the start.
Late 2018 - Should have been a radical new era changing period - either a transition like the Y2K era or proto 2020s - Some separation from earlier late 2010s was there but not enough going on.
2019 - Should have been the first proto or very early 2020s year at some point - Just a few changes
2020 - Should have a new era/decade feeling in pop culture - Barely any changes
2021 - We should be much more removed from the 2010s than we are, and feel like we are in an entirely new pop culture era - Only partial changes