Woodstock - song - was created in 1969.

That song was not played at Woodstock. The entire playlist can be found here:

http://en.wikipedia.org/wiki/List_of_performances_and_events_at_Woodstock_Festival

The group Crosby, Stills, Nash and Young performed a song titled '4+20' at Woodstock.

No song by that name was performed.

No song by that name was played at the original Woodstock in 1969. See the link for a list of all songs played, perhaps the song has a different title.