Hardware PS Vita Grainy screen

[Metroidvania96]

Hi

I have 2 PS Vitas, 1 from launch both OLED models, and i noticed the screens have this grainy or dirty look over the display. Not just some parts but the entire display, was wondering if thats the sign of a aged OLED display. They both have screen protectors, and i have removed 1 to check if it was the screen protector but it wasnt.