Over the years, Airstream kept changing the branding to sound new and improved, much like Tide! Excella's became Excella 500's and then Excella 1000's and then Excella II's, and then back to Excella, as Sovereign
and Limited became high end models. Now they are Classics...
Differences were in trim levels, quality of cabinetry and furniture, and exterior striping, etc. After enough years, the interiors and trim may not look like it did when it rolled out of Jackson Center.. (Hopefully...)