Is there any indication that this canoe has been repaired before? Shelldrake's suggestion makes sense, especially if it was done during a prior restoration. I don't recall ever seeing a build record notation referencing port or starboard. Bow and stern or right and left were the commonly used phrases. Do the B and S positions align with the current bow and stern or bow and starboard? Do you know if the initials of the current or a former owner were BS?
Benson