This knife is another hard to find model of the M9 bayonet series of knives.
I looked in the book by Richard Neyman M9 BAYONET-THE AUTHORIZED HISTORY. On page 303 it shows a 1987 M9 Buck 188 U.S.A.>and on the reverse side M9 Phrobis III U.S.A. Pat. Pend.. I read a little and on page 306 it says " The Four Line Civilian 1987" is similar to the three line but with addition of the patent pending marking. The reverse side of the 1987 civilian looks exactly like a three line version. The amount made is on page 301 and total of the exact same knife is 14,495 made from Jan. 1987 to Dec. 1987 This number includes both variations. That's approx. 40 - 50 knives per day.