"so what is so perilous in 'duplicating the conditions' in a controlled and aware manner?"
Fractures and faults like the one that is suspected of being present have a nasty habit of slowly propagating until without warning they fail catastrophically. Unfortunately it's very difficult to predict when such a catastrophic failure is going to occur so every time you pressurize the container with hot water there is a risk of catastrophic failure that could have dire consequences.
A case in point were the explosive decompression and breakup of the DeHavilland Comet aircraft during the early days of jet travel.
"What level of certainty is there in the experimenter first learning the polarizing art, then applying it successfully enough to guarantee the detection of a fault, in absence of the heat and pressure it 'apparently requires' to manifest?"
That's a good point and pictures are worth a thousand words so I decided to have a paly and see what could be achieved and how difficult it was to do.
What I did was to tape and old CD cover to the LCD screen on my computer. LCD screens use a polarized light source so you don't need to mess about with sticking a lens over a torch if you have and LCD screen, all you need to is get a blank white image on the screen.
I then viewed the CD cover through a polarizing filter that I rotated to achieve the maximum contrast and recorded the images on my mobile phone.
Here are the results.
Subsequent close inspection of the cover revealed a small difficult to see crack that radiated from the upper left corner downwards parallel to the edge. It also showed a small inclusion (bubble) near the bottom edge where the colours appear to be radiating from.
So, considering how easy it was to do and how dramatic the results were, I would hazard to say that with a little experimentation any flaw like the one described would show up like a neon sign even without the added heat and pressure.
An elephant is a mouse built to government specifications.