Airstream made the mid bedroom 27' model with optional twin beds thru 1988. They also made a few rare 32' mid bedroom models with twin beds between around 1990 or so, but I don't remember the exact year(s). These two lengths would be the last mid twin models.
25' and shorter mid twins probably weren't made past about 1981. A mid twin 31' may have been made into the mid 1980s, but rear beds were becoming more popular and I don't know the exact ending year for mid twins on that length.
Wally Byam Caravan Club International Historian
Vintage Airstream Club Historian