M_Boats: Dumb M15 Number Question

I bought my Montgomery 15 about a year and a half ago. On its transom is MMP153690686, which I think means it is a Montgomery 15, serial 369, built in June 1986. It came with red, white, and blue sails with the number 368 on them. When I managed to rip the old main about a year ago I bought new sails. When I did I couldn't figure out what numbers were right so didn't get any numbers on the new main. If I had, which should it have been, 369 (the serial number) or 368 (the old sail number)? Thanks in advance, because whenever I start thinking about this it bothers me! David Grah Bishop California