When The Grateful Dead were invited, their manager wanted the promoters to add another act he managed; he offered them two. They tossed a coin, chose Santana, and the rest is history. There is no Santana music in this movie, but perhaps they are subtly represented by the act the promoters did NOT choose, It's a Beautiful Day, with their hit "White Bird"
Much of the licensed music in the movie is by acts who performed at Woodstock, but two famous names associated with it actually were not there. Joni Mitchell felt she had to decline her invitation, but later composed a song ("Woodstock") about the festival. Big Brother and the Holding Company were never invited. Janis Joplin had left them the year before, and she performed there with the Kozmic Blues Band.
Danny is reported to have been stung by wasps (which do not lose their stingers), but Danny was actually stung by hornets (which do lose their stingers).
During the scene where people are watching the moon landing, the TV image shows the Moon's surface taken from the LEM as it descends and lands. This video was not available for viewing until after the astronauts returned to Earth.
On July 20, 1969, the moon was only 6 days old - roughly a half moon as viewed from the film's location - and would have set by 11 pm, but on the night of the moon landing, they show a full moon, high in the sky.