Believe all were made on a 2004 Dodge Sprinter 2500 with a heavy duty steel (versus fiberglass) front transverse spring. Were imported to the US up through the end of 2006? Some later units may have been designated as 2006 Airstream models (not sure).
Mostly minor changes during production run. Difficult to track down when changes were made.
Earliest units had seat warmers, blackout tape between the middle and rear windows, Fiamma awning installed by Westfalis, steel wheels, and regular rear antisway bar.
Later units lost front seat warmers and blackout tape between windows, gained heavy duty rear antisway bar, alloy wheels, Airstream installed Horizon (Fiamma rebranded) awning, change in Airstream lettering (later units had blue shadowing on letters), gray (versus beige) AC ducts in rear AC cabinet, and change in Airstream installed phone/cable jack outlet (dual doors versus single door), Airstream installed extra options like running boards, grab bar handle on upper kitchen cabinet, etc.
The Airstream installed TV model changed manufacturer (and possibly the microwave manufacturer as well).