In my document if I mention the first time "File 1234 (in the Official Records hereinafter)", then after that in the same document if I say "File 5678", will that mean that "File 6789 of the Official Records" too? Or how could I do this?
2You could use an early sentence announcing that all files you refer to are from the Official Records. The word hereinafter is old-fashioned.– Yosef BaskinMar 15 at 17:50
1Why would "File 5678" refer to File 6789?– MarcInManhattanMar 15 at 18:08
As Yosef notes in a comment, hereinafter is very old-fashioned: you'll only ever find it used today in formal legal documents like leases and statutes.
I would say
... File 1234 (All files cited are from the Official Records unless otherwise indicated) ...
If there are no exceptions you can omit unless otherwise indicated.