Factual error: Kevin and Wayne's bedroom shows a Beatles poster of the White Album. However this album, and presumably the poster as well, didn't come out until November 1968. This season opens with the summer and start of the school year 1968.
Factual error: Paul and Kevin go to the book store to buy "Everything you always wanted to know about sex." In this episode it was still 1968 but the book was not released until 1969.