I'm happy you picked this up, that thing looked complete. My vin is stamped 0481, so I know they started before 500.
There were multiple frame types, as best as I have been able to piece together: The first generation (white frame) did the single mount front only canopy, the first revision (red frame, maybe yellow?) to that modified the canopy to mount on the rear as well and redesigned the steering column. Second generation (red and yellow frame) removed the front steel plate at the head tube, built-out the front of the frame at the sides to incorporate the plastic front fairing and revised the floor for the passenger and engine mount. This is when the doors became an option. The first revision to that modified the rear to have a more boxed out fender design. Third generation (yellow frame) changed the motor mount to accommodate the Tomos A3 to replace the Minarelli V1; although, this could also have been changed with the boxed out rear fender design. There is another revision that had an electric motor as well. I'm sure The Chefhockey (Triped Dave) may have additional info...
There was a show in New York or Chicago that featured these American Triped Microcars along with other accomplishments of the designer Stuart Pivar, not too long ago...within the last two years I believe.
The picture you've included is from a parks and recreation department that bought these for their fleet of park maintenance vehicles...what a great summer job that would have been!
Please post up the sales brochure...we really should start a wiki on this and record the VIN #'s, much like the Puch limited wiki.
It's great that you have two (Gen1.0, and Gen2.0) as you can really see the major frame redesign...that white one needs a lot of work, it would be easier to hot rod with no butt hurt from the purists...HA!