I tried taking a pic but it doesn't come out too well when showing the surface of a disc.
You might be right about it being stress marks (though I'd like to hear more about this). It looks like they come from the factory this way. They look like faint almost water like stains / swirls if that makes sense. Usually it's not a big deal but recently concerning a disc I may purchase, the seller said the disc has swirls which happen when a disc is played often which I found to be a bit odd. So now this whole thing has me curious as to what the deal is with them. I also heard this can happen from leaving a disc too long in the player. Like i said, now I'm just pretty curious as to what the deal is.