With some of the openings it may be a “designers choice” to have them very tight or possibly more open than measured to make it easier to place the screen protector - users may not be capable of 0.1mm accuracy . Width and length are bit different. Of course it differs if it’s a flat film or something more specific shaped.
You are aware that a company already makes screens?
For those that skipped reading your post:
On top and only on top of the inner measurement someone can fully attach any screen protector. My post was in addition to your post referring to this screen protector edge (and if offered somewhere else please let me know):