Agreed, assuming the subdivision truly is just a more hidden version of the SR system, it is entirely possible to remain in the same subdivision assuming the equivalent net SR change is below 100 SR. However, this is under the assumption that ranks are being adjusted at all, of which there have been several separate bugs in the past that prevented ranks from being adjusted. Given the ambiguity of the subdivision system compared to the SR system, it may very well be the case that these players are experiencing one of or a new manifestation of a rank adjustment bug, hence all the claims of an adjustment bug in his thread. You can read more about those in the posts listed in the megathread under the subcategory: Incorrect Rank Adjustment: The Competitive Bugs Megathread.
Thanks for catching that, I’ve updated my previous post to be a more accurate.