I haven't had any luck searching for this...

I recently acquired a pair of used SP cylinders and heads. Knowing of the R/SP differences, I checked the cylinders, but one of them has no "L" cast into it, the small circular spot is completely blank. It also lacks any serial number stamped into the opposite side (all my other cylinders have this). I have measured the deck height, and it is an SP spec. Visually, it appears identical to all my other cylinders.

Could someone in the know shed some light on why a cylinder would not have any H or L markings?