Good find.....
Quoted from Wikipedia "The more-than-six-minute song was not released as a single, as Wonder was unwilling to shorten the song to fit the 7", 45 rpm format. With consumers demanding a single, Tamla compromised in late 1976, and a promotional version was given to radio stations. This edited version, 3:12 in length, received so much airplay that it reached number 23 on the Adult Contemporary chart in January 1977"
Interesting, since numerous hit songs indeed exceed the 6 min threshold for a 45 release. "Hotel California", Hey Jude", "Like a Rolling Stone"....etc... Stevie could have released this as a single and it may have reached #1 in early 1977. The 3:12 time for this promo single is a tad short, compared to what radio stations air today with the cold ending that runs nearly 3:30. Take that or radio stations would have to edit out the baby sounds on the 6 min version.