According to Edith Reiter's 2014 book, this instrument was completed on 9 November 1906 and sold to a customer in an unknown location.
Howe & Hurd (2004) describe heckelphone #26 as a model 36a. As of 2006, it was reported to belong to bassoonist Harry Searing, USA, who played it with the New York Philharmonic. Previously (likely up to 2002) it belonged to the Yale University Band and was used in the New Jersey Symphony.
The earlier history of heckelphone #26 remains largely unclear.