Browsing the listings at Christie's musical instrument auction in NYC on May 16, I noticed the following description for Lot 15:
GIBSON MANDOLIN-GUITAR COMPANY
A MANDOLIN, STYLE F-4, KALAMAZOO, CIRCA 1924
Labelled Gibson Mandolin Style F-4/Number 75677
No photo unfortunately. Price estimate of $3-5k sounds a bit low to me.
Elsewhere in the auction, there's a 1918 K-1 mandocello (Lot 38) .