It's very difficult to see any clear image of the ---CZ factory's 'stock' retainer pin in an original condition--- (often called the slide's Roll pin) on Google - or Youtube.
I've used both a smaller and a 1/8" punch (with tiny ball on the tip) to push the Retainer -most- of the way out of the slide.
This tiny 'slot' might be an original feature of the CZ factory's Retainer pins? The length of this slot is only a fraction of the length of the Retainer pin.
Note: I don't know how to upload images, but can easily text an image to another smartphone.
Facing the left side of my gun, held horizontally, looking directly at the mostly-removed pin, the "slot' is at approx, the 4:30 position. --------
It is similar to this (blurry image at :51) short "slot", and according to this SP-O1 owner, No similar opening should be there.
-----------

-----As a precaution, I would like to order a few spares from CZ USA (if located on website), because my pin seems to have a visible glitch from 'moderate' dry-firing.
Apparently they are Sold Out -- if the Outer roll pin is the correct nomenclature.
"CZ Custom" has a 75B firing pin retainer pin....must be the exact type used in the PCR (75D) ?
https://www.youtube.com/watch?v=0dyE1x8nMwA