If there is a reason, significant or otherwise, for the left-handed tang stamps of some of the earlier SW sheath knives, it escapes us here in this new century. Perhaps a hint lies in the early left-handed sheaths not uncommon earlier, less common later. Why left-handed sheaths? I've asked a lot of folks including Mr. Levine and no one knows for sure. Conjecture ranges from the idea of wearing a sidearm on the right, to clearance for right hand carry of a longarm (rifle or shotgun), to just simply a fad of fashion with users of the earlier era. It does make sense to use a left-hand stamp with a left hand sheath (presentation of the maker mark upon drawing the knife), but... why use them with right hand sheaths?
Why split the marks between the two sides? We could make a guess. SFO's such as those for Sears etc. seldom used the SW pattern numbers, and by adding them to the off-side the same blanks could be used for either SW or SFO. I have several examples where the pattern number is an off-side etch. The Craftsman mark did not appear on pocketknives until the WWII era and then as a blade etch, not a stamp. That came later. And the use of Craftsman stamps on sheath knives came much later, 1960's approximately. Until then custom etches were used with standard SW tang stamps even on Ted Williams knives. Speaking of which, Ted Williams knives were made from circa 1961 thru the late 1970's. Have you ever seen one stamped Ted Williams either in block text or signature replica? Why not?
Michael