[CR]1st Gen. Dura Ace track hub marking?

Example: Component Manufacturers:Avocet

From: t.kielman@comcast.net
To: classicrendezvous@bikelist.org (C.R. LIST)
Date: Fri, 22 Oct 2004 00:20:11 +0000
Subject: [CR]1st Gen. Dura Ace track hub marking?

I have a set of the satiny high flange Dura Ace track hubs,I believe 1st generation.Both hubs have a letter Z and J marking on the barrels below the stamped Shimano logo.Any ideas as to what these markings signify?
   Cheers, Todd Kielman Chicago Il.