It's always fun to look back at beginnings. Here's a piece by Pullum trying to place a date. IMO, though it's not that important to answer this question correctly (there may not be a correct answer), it's fun to think about for it returns one to important landmarks and allows one to remember important contributors whose fame is not what it used to be. Take a look at the comments section. Avery makes a showing and Robert Lees important fillip is justly recalled.