Glass etching?

[70runner]

Purchased passenger side qtr and door glass for the RR about 6 months ago. Inspection of the pieces prior to install showed no defects, etching, or otherwise. Install was big job, but very careful with the glass. RR has been in the garage since, with a cover. Today I was working on the RR and noticed spots on the qtr glass. Cleaning didn't remove them, so I ran a razor blade over them, still there. Definitely etching. Exam of door glass showed same thing, about a dozen spots each. No etching on OE driver side glass, 10yr old windshield/rear glass.

I'm at a loss to explain this. Is it possible for glass to etch over time, perhaps a manufacturing defect? I'm 99% certain this etching was not evident when I unpacked the 2 pieces. Plus I would have noticed a dozen or so spots even with my old eyeballs.

Glass when unpacked...

Same piece now, with some black backing to show the etching spots...

 

[vance.dykes]

there is some glass polish out there maybe it could remove.

 

[Frank Mopar]

What I usually see is someone shooting grinder sparks at the glass, car etc. The sparks embed in the glass and start to rust.
Not sure if thats what you have but its a word of caution when grinding.