A lot of interesting responses here!
@jc4659 I HAD to look up Monty Python's Matching Tie and Handkerchief LP with 3 sides. The interesting explanation from Wikipedia is:
"The album's original LP edition is particularly notable in that it was mastered with two concentric grooves on side two, so that different material would be played depending on where the stylus was put down on the record's surface. For this reason it is sometimes referred to as a 'three-sided' record."