The glass did not have any
The glass did not have any sign of the cracked shelf under it – no creases etc. I was using shelf paper 1/16″ under the glass and around the stainless molds. I assume it cracked on the way down because there was no healed marks on the bottom of the glass. I did discover a crack forming on the 6×6 piece but not the other one after a few days.
I may have been aggressive taking the glass out of the the stainless dam (which I did in the kiln and on the shelf).
The shelf was thinner than most (I got it second hand – made in taiwan with riddges on the bottom).