How I Group the '90s Decade Eras

Thanks to the help of the community I've figured out how to group the '90s. These are the eras of the '90s.

1991 - 1993 - Early '90s

1994 - 1995 - Mid '90s

1996 - 1998 - Late '90s

The shift years would be 1991, 1993, 1995, and 1998. 1990 is an '80s year culturally and 1999 is a 2000s year culturally.