There are some instruments from after 1905 which differ recognizably from the standard design of the Models Nr. 1-4. One of these instruments (Custom Model 3) is documented in four specimens (all instruments come from about 1920). It can therefore be guessed that Boehm produced this type of instrument for some time in series without finally establishing it as a further standard model. A special case is of cours the instrument with the aluminum neck for which Boehm received a patent in 1914; until now, it is documented only in a single instrument of the Nr. 2 type.
The other custom made instruments are only documented with a sigle specimen so that it could be the case that Boehm built them individually according to the wishes of his customers. One early instrument from ca. 1906 is also quite interesting for its head is also inspired by the Guitarra Portuguesa, but this time not by the Lisboa type (with its scroll head) but by the Coimbra type.
