I switched out a number of B17’s for their X versions which I found to be far more comfortable. Only thing I’m curious about is there appears to be a significant amount of stretching taking place.
As I’ve noticed the adjustment bolt becoming loose and rattling or squeaking, I’ve tightened it to the point I can feel solid contact at the nose. On one of my bikes I’ve done this now 3 times in the last two weeks, is this a normal level of stretching or am I doing this wrong ?

Actual owners will probably weigh in but I've read that this is considered a "feature" rather than a flaw and the thing will need periodic adjustment indefinitely.

It's as predictable as sunrise.

However...

Don't overtension
Don't retension when damp.
The saddle will never feel stiff, like a B17. If you attempt to achive that feeling, you will be overtensioning the saddle.
You may want to consider lacing it, as I did.

Good advice above. You could use locktite on the threads or double nut if there are threads enough.

Tighten it until the narrowest part of the slot cutout has about 1/4” gap. 1/2” is too too tight. Both of mine don’t need adjustment but one a year or so. https://selleanatomica.com/pages/setup

I had to adjust mine several times initially but haven't had to do so in probably a year now.