I have never heard of a Discovery I. I've always understood that the Discovery series began with the Discovery IIs.
Here is a timeline of the Discovery series I compiled (they may have all had 8.1A ratings--those recorded are the ones I know for sure did) Years are approximate since Aerus has made its records available to the public, so they are based on observations:
Model 1500/Discovery II™ - sand/jade: 1986
Model 1500C/Discovery II™ - sand/jade: 1986
Model 1572E/Discovery II™ - sand/jade: 1987
Model 1572E/Discovery Plus™ (8.1A) - sand/jade: 1987 ("Plus" stood for onboard tool storage)
Model 1572E/Discovery III™ - (8.1A) sand/taupe: 1987-88
Model 1572E/Discovery Advantage™-lt.sand/navy:1988-90
None of the series had headlights--which were added during the later Genesis upright series.
Those with the bold, capital letter wordmark--Discovery III and Discovery Advantage--were manufactured in Canada and assembled in the U. S. All the others--with the familiar boat-shaped logo first used in 1962--were manufactured and assembled in the U. S. The Canadian and American companies merged around 1985, and the Canadian plant closed 4-5 years later.