The thread is getting into more interesting stuff as it progresses.
Re what this and that - to the extent we can reasonably infer, it is necessary to look at the TCDS for a specific Type/Model. This will have the basics of the frozen design standards applicable to the certification and some details re backroom agreements. While one can't be sure that one can infer the whole story, the exercise will give you a pretty good picture of what's what..
See the FAA website
https://rgl.faa.gov/Regulatory_and_G...meset?OpenPage and play a bit there to get to the nitty gritty.