Hi Charles,
I had to puzzle for a bit to figure out what you were talking about, but a visit to the Javadoc man page revealed this:
The Java Software convention for the argument to the @version tag is the SCCS string "%I%, %G%", which converts to something like "1.39, 02/28/97" (mm/dd/yy) when the file is checked out of SCCS.
Ah! SCCS is an (old-fashioned!) source-code version control system, like CVS, Perforce, Subversion, SourceSafe, etc. If you put "%I%, %G%" into a text file and then store that file in SCCS, when you check it back out, SCCS will expand the text to the file version and date, as shown; the checked out file will no longer contain the "%I%" stuff, but the actual version number. Javadoc will then dutifully use the expanded text to produce documentation. Nowhere in the Javadoc documentation does it mean to imply that Javadoc uses this syntax for anything -- it does not!
Some other version control systems have similar magic tags; for instance in RCS or CVS, you can use "$Id$" to do something very similar.
In any case, if you're not using one of those source-code control systems, then just use an explicit version -- if you feel such a thing would be meaningful.