They're still out there, waiting to be found...
My cousin restores cars at the Auburn Cord Duesenberg Company in Oklahoma. They recently found a 1931 Duesenberg Model J, with a disappearing top body by Murphy, one of 25 built. It's been sitting in a garage not seen by the public for the last 50 years.

A video has been posted showing it getting hauled out of the garage, my cousin is the guy in the blue shirt briefly shown at about 1 minute 30 seconds in:
https://www.youtube.com/watch?v=1nIRP9hP9rQ