@Pieter1982NL Aha, I think I start getting it. At least, I hope! Correct me if I’m wrong.
Finding the correct variables or events is indeed a puzzle - something that can only be done by real experts (not me - at least not yet 
). But the results of that groundwork can be found in MobiFlight, because one of the nice features is that it contains a downloaded list of all known events and variables. This list is continuously been updated by the community, and can be downloaded with one click of a buton. Am I right?
Below for example, I could find all the INC events for SPD, HDG, ALT and VS.
Looking at the above screenshot, is it also correct to assume that some events are native FS2020 events (the ones starting with “A320”), and others are proprietary for the FBW A320NX (the ones starting with “A32NX”)? Means that FBW uses the FS2020 events if they can, but only replace the ones they need to adapt to their model?
Just trying to get my head around it. And if the above is true, then I start understanding your quote at the beginning of this post:
I start believing that you are a wise man @Pieter1982NL