I recently added the below prefatory note about sources to the beginning of the Alto Trombone Timeline.
A note on sources: In historical research, primary sources are gold. Why? Because they bring readers closer to actual documented facts rather than individual interpretations and opinions. The timeline below draws from more than 85 primary sources, which is, I daresay, more primary sources than any other single document on the alto trombone (with the possible exception of bibliographies). In addition, the timeline utilizes numerous current secondary sources, including Early Music, Historic Brass Society Journal, Galpin Society Journal, and a number of recently-published books. If you notice a source in the timeline that you feel has been somehow discredited or improperly vetted, by all means, let me know, and I will consider correcting or deleting the related entry.