My Sax repair man commented that my 1919 Buescher Tenor doesn’t have a “Front F”, a key which would let you jump fourths between top C and top F without having to squish 3 keys with your left palm.
It turns out that Buescher introduced the Front F (also know as “Top F”) in about 1925. There were a number of innovations to the key mechanisms on saxophones, as well as clarinets, to extend the range and to make certain notes or intervals easier to play.
The “Saxophone Museum” records models, date of manufacture and the serial numbers of many saxophones, and has a large collection of photos that helped me identify when Buescher added the Front F. Another useful reference was photos of instruments for sale on Ebay!