And the eBay listing of the model 18 photos for future reference followed by a 1977 ad and a 1968 news blurb (I found nothing for the Janitronic or Sani-Sweep):
According to the serial number, they changed from the Irish emerald green and white color scheme to the D80 green beginning at serial no. 10001 (not 110001 as I mentioned years back), and I believe the first year for that was back in 1972.