I have gunsmithing and reloading books that date back to the 1920's. Headspace was clearly understood and defined back then. It was understood by most well before then but standardization issues is what brought about the Society of American Manufacturers of Small Arms and Ammunition (SAMSAA) in 1913. In the 1920's SAAMI took over in fulfilling this roll. https://saami.org/about-saami/history/
No convincing needed for gunsmiths or reloaders. They just looked at the specs.
On that you are correct. Yes, someone just made that up. That would be the designer of the cartridge.
You also need to look up the definition of what an artifact is. When you push a shoulder back the old shoulder is not an artifact. The old shoulder simply no longer exists.
If I thought you were actually serious I would be willing to continue this discussion but statements like this
indicates this is nothing more than trolling. It's applies in your mind only. Must be nice to know what millions of reloaders are thinking.
Your premise is easily disproved since for as long as people have been pushing shoulders back these same people have been stating the need to neck ream or turn due to the increased wall thickness of the newly formed shoulder when you push shoulders back.