No, I'm not missing the point. I understand that a crystal that is compromised can be bad for the integrity of the watch in any environment, not just when in the water.
I guess that the question then becomes: Lots of people on this forum have T-39s on their (great!) timepieces. So, it must just be then that their crystals are do not lack integrity/have minute fissures? If so, then there must be some T-39s out there that are OK to put in your watch and still have great integrity? That's what I'm wondering, b/c I often hear conflicting accounts/opinions on these older crystals.