manufacture date (traditional estimates)
1917 shipment date, according to Spann's Guide to Gibson
Mandolin, Style F4
Factory order number unknown
Nice redburst F4 here to demonstrate the "hidden serial" number
From Gryphon Strings.
Frank Ford is on of the founders of Gryphon Strings. Frank is world-renowned as a master repairman and an expert on vintage mandolins. Gryphon often carries very nice vintage mandolins. Frank is also the author of Frets.com, a website well worth the visit for instrument fans, luthiers, and repairmen