The 5685, (I'll call it stock number), shows up around 1992. The 5685 number was used to identify the version of that pattern that was marked with U.S.M.C. very similar to the way many of knives made during WW2 were marked.
They made this version of the knife from around 1994 till Camillus closed. They made the 5684 and 5685 simultaneously during that time. They were just marked differently.