If you don't mind the "car" metaphor... Not all cars produced by Chevrolet in 1957 were Corvettes...
This Kohlert horn does seem to have a 1957 serial number... But that doesn't automatically make it a "The Kohlert '57" model...
There are lots of little bits and pieces about Kohlerts all over the internet. What makes them difficult to find is the fact that the name (Kohlert) is being used for cheap Asian horns now... so doing a Google search returns a bunch of stuff that will confuse you...
I have seen some evidence to suggest that the NON-57 horns were called Bixley's or just Kohlert, there are other web sites that suggest there were lots of model names (none of which I can recall now) but those names may have been used in years other than 1957...
It is still a good playing 1957 horn, but it’s just not the pro level top of the line Kohlert from 1957...
ENJOY

This Kohlert horn does seem to have a 1957 serial number... But that doesn't automatically make it a "The Kohlert '57" model...
There are lots of little bits and pieces about Kohlerts all over the internet. What makes them difficult to find is the fact that the name (Kohlert) is being used for cheap Asian horns now... so doing a Google search returns a bunch of stuff that will confuse you...
I have seen some evidence to suggest that the NON-57 horns were called Bixley's or just Kohlert, there are other web sites that suggest there were lots of model names (none of which I can recall now) but those names may have been used in years other than 1957...
It is still a good playing 1957 horn, but it’s just not the pro level top of the line Kohlert from 1957...
ENJOY