25 years of parts support, according to their website.
It's a bit difficult really to try to construct a dated model timeline for Greenfields. It doesn't help that there aren't even publication dates on the Parts Lists that ODK have been able to obtain.
We can say for sure that the Anniversary models came out in 1987, as that was the 21st anniversary of the firm's start.
I'd guess that the Evolution 2000 came out in that year, but I'm not sure where it fits in the overall Evo series...
And that the earliest models were the:
HD-x [x=nominal horsepower; 6 or 8] Series 1 Red, all G65 Honda engines; Series 2 Yellow, G65 Honda or Fuji Robin EY25D.
1967-early 1970's. It's been said on ODK that there was a slightly different version for 1966 only, but no example has so far turned up.
Mini-Tractor series; 5 and 8 hp Briggs vertical shaft recoil start, with 160cc Victa industrial engine as an alternative [never seen one of those!]. Early 1970's
Tractor-x series; model numbers x VR for recoil start, x VE for electric. All Briggs vertical shaft engines - 5, 8 and 10 hp; the 10 was later replaced by 11hp. Mid 1970's
