Lol I was in the business for 10 years. Cr39 or polycarbonate is the most common material. There is a high index, I forget what the material is, for higher prescriptions because you can get the material thinner. Glass isn’t very common, it’s more expensive, it’s heavy, it’s thicker, and it’s fragile. I’m not saying you don’t have glass, it’s just not the most common material. Very possible there was a notation made on your script by the optometristic telling the optician you need glass and that may be why you’ve had glass this whole time.