My theory is that once the fluid boils the first time, it is able to easily get 'around' and breach the seals of the CSC. Note, I have never held a CSC in my hand, just mentally guessing how it's built in my head.

Once the seals are breached the first time, assuming you don't have a catastrophic failure right there, right then, the seals are now significantly weakened and the CSC is on borrowed time.

I had the dealer replace the factory fill DOT 3 fluid on my 2020 with Motul RBF600 before driving off the lot.

We will see if the car having only ever been driven with RBF600 since new along with an annual RBF 600 fluid flush (summer driven car only) keeps the CSC in good condition.