Interesting and puzzling, to say the least. I admit to being flummoxed by the 1991 knife in an ostensibly 1996 or later box. So allow me to do some speculating.
From the Ka-Bar website,
http://www.kabar.com/history.jsp
1982 Cole National Corporation falls into a period of business difficulty that puts the company into bankruptcy. During liquidation the Ka-Bar product line is purchased by American Consumer Products and moved to Solon, Ohio.
May 1996 The Ka-Bar product line and assets are sold to Alcas Corporation of Olean, New York.
June 6, 1996 The acquired assets of Ka-Bar are relocated to Alcas Corporation's Olean headquarters.
Any chance that "1991" commemorative was actually made in 1996?
1975 As a part of its efforts to revive the company, Ka-Bar establishes a special Collectors' Division. Its purpose is to produce significant and commemorative knives, to recreate famous antique Ka-Bar knives and actively support the development and enjoyment of knife collecting in general.
1976 The first knife is produced by the newly formed Collectors Club: a full dress version of the USMC Fighting/Utility knife, produced in limited number.
The company had undergone an earlier bankruptcy in 1961. Ka-Bar underwent a very stormy and tumultuous history of moves, name changes and financial difficulties, if the company website is to be believed.
Perhaps due to the turmoil of bankruptcy and acquisition they missed a few years of commemoratives and then went back and filled them in afterwards, as a quick source of revenue for the new owner. This is just pure speculation on my part.
Any way you look at it, a beautiful knife with a cloudy, enigmatic history. A knife with a story, a collector's dream.
http://www.kabar.com/history.jsp
http://www.alcas.com/history.htm