Re. red #s on front of AS ?
If you are really concerned about the "one-owner" status of the coach that you are considering, you might try contacting the DMV and request a title search (assuming that the trailer is located in a strict title state) - - there is usually a modest fee associated with such searches.
I wouldn't be too concerned about the incongruous numbers. The recent issue numbers have a habbit of doing strange things as they age - - one of the ones on my Overlander simply fell off after about three years of use. It is possible that one of the number may have fallen off, or it is also possible that during rountine replacement the numbers may have been shifted left or right by the person applying them. The scenario of an interrupted membership in WBCCI is also quite plausible. Another possibility that might be that the coach is a "One-Family-Owner" translating into more than one individual from the same family having owned the trailer since it was new.
Unlike used cars, it doesn't seem that one-owner Vintage Airstreams are necessarily preferrable to one-owner used cars for instance. While my most recently acquired Argosy Minuet was a one-owner as verified by original regristration and purchase documents included with the traqiler, it wasn't one of my primary reasons for buying the trailer - - the trailer was well maintained and was being offered at a very reasonable price.
My '64 Airstream Overlander came to me with three previous owners - - the first of whom were friends of my family who took me on my first camping trip in the trailer when I was 5 years old. I didn't know the history of the trailer when I bought it - - the trailer just happened to be in very good condition at what seemed to be a reasonable price. Unless being able to own a preious "one-owner" coach is extremely important to you, I wouldn't get overly concerned about the actual number of previous owners.
Good luck with your decision!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)