Dating vintage martin guitars
Transition started in 1926 with O-17H according to Longworth.
1929 Martin switches from rectangle to belly bridge (Longworth 2nd ed page 84) 1930 Oct, first time size & model number stamped on neckblock.
Sometime around here Martin starts putting the Martin decal on the front of the peghead.
The size and style designation was written on a paper label, glued inside the top of the instrument case.
Some pre-1898 guitars have the date penciled on the top just inside the sound hole.
1920's Martin transitions away from pyramid long bridge to standard long bridge on 18 & 28 series. 17 series either never had pyramid bridge or transitioned earlier. Some lack Martin Serial #'s or markings of any kind.
1929 18 series Martins fully switched over to nitro cellulose lacquer finish.
Search for dating vintage martin guitars:
Heel block on this one stamped 1939 switch to narrow necks (1 & 11/16ths) at serial #72740 for 000 and D models.