We found 3 models of the Sovereign by Airstream listed with NADA for 1974. Each has a different weight listed with NADA Guides: 4915, 5035, 5005. ALl other dimensions (length: 31 ft) are the same.
We have included instructions below to find a blue book value for a 1974 Airstream.
Go to [www.nadaguides.com]
Select = [RVS]
Select = [Travel Trailers/5th Wheels]
Select Manufacturer = [Airstream]
Select Year = 
Select Model = [Sovereign-D]
Enter Zip Code = 
Options = [Select]
[Get Base Pricing]
Suggested list price = $10745
Low retail = $7450
Average retail = $9000
All 3 models of the 1974 Airstream Sovereign had identical values when checked