The RtLS by Switch Year
Here is when respondents to The Road to Lisp Survey made it to Lisp, just one of several taxonomies found on The RtLS All-Kenny Page. When multiple visits were reported, I went for the one that seemed like the "never looked back" visit.

2003 (24)

2002 (28)

2001 (10)

2000 (7)

The 90's (21)

The 80's (22)

The 70's (3)

The 60's (1)