68 Road Runner Speedo Lens Lettering-Some With or Without???

Why do some RR, GTX, Coronet 68-69-70 Speedo lenses have the switch calloouts on the lower lens?

Different Suppliers? There is only 1 part # for the lens in the 68 Parts Book???

I recall using my as bought in '97 lens. when googling pics I see Hemi Cars, AC Cars, GTX etc with either lettered or non-lettering

Ive also noticed that the Speedo #'s on the Lens appear larger and crisper on the "non-Switch Lettered" lens

From what I remember it was an early (with) and late (without) thing.
Mainly because it was too cluttered with the writing.
Ron

my Car was built 11/6/67

Again as in the FMVSS regs for non or low reflective areas in front of the driver FMVSS NO. 101 called for the controls to be identified (labeled) effective (1-1-68) but NOT illuminated until (9-1-72) Maybe Chrysler decided to meet the phase in '72 illuminated regulation early in '68 and found it to not only be a little confusing (as Ron stated), not cost effective and redundant with only having to highlight in white the control name above the control. Which brings up the question if the white paint was slightly reflective and we've been using the incorrect paint forever for the labeling?????