Steve, somehow I lost your message about the hammer gun you were inquiring about with the joint check. I believe your first couple serial numbers were 77 and looking at my records, your serial number would be 1899 and the last serial number I have in my records for the joint check is 78444 also 1899. Serial number 78619 also 1899 does not have the joint check.
I hope this helps and if you could share that serial number for my records I would appreciate that.