First of all, thank you for stepping out and answering
Just for documentation sake, Pokemon Gold/Silver/Crystal had Gold/Silver/Silver foil inserts as background, specifically.
From the carts that I own with good label health it's not as shiny as a glossy photo paper and not even close to that in thickness. I also do not believe the original media to be a photo type, as as you said the dither can be very evident. It mostly looks and feels like regular thin sticky paper with a clear tape protection over it post printing but I dont believe putting tape over a print would actually work as much as a bootleg cartridge label would.
I know for sure they didn't had 600 dpi digital printing presses back then, and 120 dpi sounds about right in terms of resolution at the time of production.
I don't know. I'm very confused. I'll try ran some tests and see how do regular 80 gsm paper works if at all.