I would rather say that Sony’s AOSP binaries are never really finished and polished. They don’t get a fraction of care and polish that their stock “firmwares” do. Of which the best confirmation is the 10 III note quoted by yourself:
… which sounds like an excuse for never bringing it to a fully reliable and functional level (quite possibly on purpose).
So, whether for some device there is a “Work In Progress” note or not doesn’t really mean that those without such note are finished and complete. Maybe it’s more like alpha vs. beta. And it’s quite possibly intentional, as I bet that Sony does not really want to be freely offering an AOSP platform anywhere near comparable in terms of quality and stability to their own Android so that it can be used to build for their hardware competing software solutions.
Hence my question “what does it change” - probably not much…
I don’t know if the 10 III binaries from February, 2022 had a “WIP” mark or not when Jolla decided to use them in SFOS, but they still had severe issues like display color banding, echo, excessive power drain, and more. On the other hand, since then Sony released three new binaries for the 10 III (maybe fixing some or all of those issues) but Jolla does not use them. So it’s kind of a vicious circle.