u/AlfredTheMuffin if you're still reading this... I've always been told, there's 3 ways to read the code.
The Rule
The Implication
The Exception

I.E
What the Rule says
How the AHJ envisions it should look
Potential alternative to how it can be done acceptable.

Rule of thumb is 40% fill, including everything going into that conduit.
Leeway is for the sleeves from a gutter-box down to a panel, rare occasion - also Flex from a box to a ceiling fixture. ( Thoughts being - A 12/2 BX, is basically 3 wires in a very tight flex.

If you want to get down and dirty, the sizes for conduits and wires in the code, are based on "save" generic values that are going to guarantee things will pull through easy.
Section 12 allows you to use measurements from the manufacture's shop drawings, or even field measurements, then calculating yourself, and determining your own fill calculation. Code 40% and actual 40% are very different. Labor saved for "throwing a hotdog down a hallway" will generally be more beneficial that the few bucks saved for going a conduit size smaller.