Wow. Thank you for the official clarification.
Regarding demotion, so is it possible to get closer and closer to demotion even when at non-zero LP at divison IV of a rank since MMR is behind the scenes to the visible rank then losing just one game after 0LP suddently demotes? Or does it have to be multiple consecutive losses after dropping to divsion IV 0LP.
Also, while I have you, (since apparently the other commenters find this bit more intriguing)- Is there a short answer or a simple reason why in my case I am overall still winning more games and gaining division (gaining visible rank) but my net LP gain-to-loss (indicating lower MMR than my visible rank) is about -2 to -5? Is this normal?
Anyway, overall this means that that Riot page has falsely claimed that "MMR is a secret". Because by your explanation MMR is basically just derived from win/loss, it is not that much of any sort of a secret.. (with miscellaneous supplementary measures to increase a...