I recently purchased a Marlin model 20 pump 22 and all information ive found says they were manufactured between 1907 and 1922 but found information that says that includes models 20-a and 20-s. Mine is just a 20 with no letter. I haven't found a serial number in the usual place and some says it is actually under the butt stock. If this is the case my serial number is 2076. Can anyone confirm this and/or help me date this firearm?