Chris, that is how I determined the changes made to the hammer guns from 1883-1936. Just Fulton hammer guns, 364 (as of today) serial numbers. This is the only way to determine when changes were made along with pictures to show the changes.
There are no records that Jim has for hammer guns from 1891 to 1893, and from my research this shows that also.
Also there was a period of time between 1889 to 1890 that only hammer guns were made. These are true transition guns as they have all the attributes of a Syracuse hammer gun, but do not have a makers name on the barrels. Serial number range from 25500 (closest I have is 25627) to 29999.
The joint check stopped for the hammer guns late 1899. From my records 78619 is the first one I have that doesn't have the joint check. Serial number 79000 is from 1900, so I believe it would be the same for the hammerless guns.