LOL, you know everything. You have obviously serviced the southern California area, Phoenix, Vegas etc.
Most items have a 4-6X safety factor over their pressure rating depending on what certfications they are qualifying to. We sell membrane housings that are rated to 1200 PSI, but they are qualified to 7200 PSI. Our cheap little plastic filter housings are 100 PSI rating, but they burst on our test bench at 600. Our Stainless lines are 100 PSI rated, burst 800 PSI.
Even standard PEX tubing has a burst rating near 400 PSI at 180 degrees F, and as most professionals know, higher temperatures lower the burst rating. I can only guess the burst pressure of PEX at 80 degrees is probably in excess of 500 PSI.
T&P valves leaking all night long is a common symptom of these issues, but since most P&T lines drain outside into a garden area, it can go unnoticed. Most houses in high PSI potential areas are regulated, but when the pressure regulator fails or starts to wear out, the pressure can and does go very high in some areas.
Do you need any more information? Next time your in my area, please drop by and I can take you to some of our test sites where we have cheaters on unregulated city lines.