Second time in the A&CG forum, second time it's been about a banjo.

Once again, I have one of my dead uncle's banjos with me. It's a different one than last time. This is a Gibson Mastertone. No idea about anything else. It's 5 strings, Gibson banjo tuners, bowtie inlays on 1 and 10. Butterfly looking one on the 15, bird looking one on the 17, diamond on 12, cross on 3, MASTERTONE on 21 and mustache on 7. The headstock has a tiny cross with 4 diamonds extending out from it, a diamond above Gibson, and 2 f-holes that look like they're pointing the wrong way on the sides. There's no serial number on the back of the headstock or in the resonator, although it does have a Kalamazoo sticker.

Anyone have any clues? Need pics? What can I do to find out the year?