I know all about contra claims. I've been dealing with them for 40 years.
Like the Boss Green brigade who insist on a dollop of BG on compression joints - then wonder why the DVC doesn't work. "It's clogged up with gunk, sir, the same gunk that's on all the threads."
You are still harping on about the different configurations for O rings and gripper rings. 15mm Cross-linked Polyethylene/Polybutylene is 15mm so there should be no more problems by using pipe A, insert A and fitting B than with using pipe, insert and fitting A.
If you've been designing this stuff for 10 years give us some examples of which configurations will fail - and why.
As said on previous posts "you shouldn't mix fitting / inserts / pipe"
There are also umptydozen threads which refer to using the correct inserts and the install being OK.
I have never ALLEGED to be a plumber!
I have never advocated using anything other than the pipe manufacturer's inserts!
Not too good with facts, are you.
Who offers a 50 year warranty?
BTW, scenario is spelt s-c-e-n-a-r-i-o.