Dual number tach lens ?????

[Jens Jimmy]

I'm going through my NOS parts, selling them here on the "parts for sale" board.
I came across this lens that I didn't know ever existed. Other than having a dual set of numbers on it, it still looks different to me.
My question is, Has anyone ever seen this? Did GM really produce these? It is in a GM NOS box, PN 6458266 , which is the same number on the rest of the NOS lenses that I have sold.
Anyone have any knowledge on this?