Ooh, an 00-21!

Is it old enough to have the herringbone rosette and slotted diamond fretmarkers?

If it does, it would make a Norman-Blake-matched set with my Martin Style B 1922 flatback mandolin.

(The Style B mando was decorated like the Style 21 guitar. The Style A matched the 18 guitar and the Style E matched the 45. When Norman Blake gave an interview to Acoustic Guitar magazine several years ago, he had two such pairs of matching guiatr/mandos. One was a Martin pair and the other a Gibson.)