Consider the expected failure mode, It's in tension in the chamber annulus. An axial split - hoop strength failure. A weak spot will go elastic first transferring tension around the defect. Which, of course,, we expect to be strong enough to handle the extra stress. So you can't really go by the thickens of an annulus without a defect. No? Except, of course, it's definitely safe if the thickness at the defect is at least a thick as a sufficiently thick n unaffected annulus, all else being equal.
