Humm
I guess Fabrizio was right, and while waiting for Bill answer, I can only say that my very first M9 has (well, better say "had", as it was soon replaced) a dummy pommell, that is quite different from yours.
See pictures here:
http://www.quarterbore.net/forums/showthread.php?t=723.
What I believe, based on the answers in that post, is that the dummy pommell I have is the same of the M9 Field Knife Japan I.