I have read this entire 15 year-long thread, and I don't think I understand anything better than I did when I searched up the same question as the OP.
No fault of the posters, though people tend to add bits of extremely minute partial detail in dribs and drabs, probably based on their particular experience.
I think really you'd need a well written and edited book with diagrams to properly explain the history of and current naming conventions for tires and wheel sizes.
In any case, speaking of personal experience, I just installed a 45mm winter tire marked 28" on a rim marked 29, which I bought because I was told it was the same as a 700.
It fits fine! All perfectly rational