1981 to the present for the setting (Greyhawk) and presence of some characters (now long since become NPC's).
I'm currently running three campaigns in this setting:
- #1 started in 1996. 3 out of 4 PC's were there from the beginning, converted to 3.0 and 3.5. But haven't played since about 2005.
- #2 started in 1998. Still going strong. Of the 9 PC's, 5 started in 1998, 3 are from players who joined later, and 1 is a replacement PC from the 1996-started campaign, been in use since about 1998. All PCs were converted to 3.0 and 3.5
- #3 started in 2004. 3 out of 4 PC's were there from the beginning. All are 3.5 native.
Now you can see why I'm not a fan of edition changes.