By the way, I also know this ^ is a whole debate in itself.

I've always understood the label as referring to season (i.e. BBAU 2012 should be BB09 and 2020 is BB12)... but more often than not I see the year being used to refer to seasons instead (i.e. 2020 as BB20 or 2025 as BB25).
We just got lucky in the first few seasons on Ten where both the year and season number coincidentally aligned, so those are universally agreed on. Anything after BB08 seems to interchange depending who you ask.
In my view, the upcoming AU season would be BB16, unless specifically using the full year like BB 2025.
Yeah I think the simplest way for the casuals moving forward will be the year, its only really us the hardcore fans that will know/care much about the technical season numbering, most of which way you personally like to term them are also valid, even with the gymnastics of working around that patch of complicated history with an asterisk of the 7 Era being a big deviation in format. I.e This year would just be as well to say its BBAU2025, The 16th season of civilian Big Brother overall in Australia, The 1st Season of the Channel 10 reboot, The 9th Season on Channel 10, The 12th Season of the Live/as it airs format, BBAU16/2025... and so on.
As you say the initial years were easy because the season number lined up with the year, and BBUK had one year number behind the season as they started in 2000, until the gap between C5/ITV, CBBUK had a a few breaks and a skip cause of a specialist season, then doubled per year from 2012 with Winter and Summer editions (which could also be an indicator used for some shows airing seasons twice per year, or maybe as .1 and .2, using a series sub-title like Survivor AU did, etc) and overtook the main series numbering and now with the 5 year gap its CBB who now has their year of airing one more than the season numbering, and also it now happens to line up with number of years since CBB1 aired.
I also notice theres a bit of a difference between currently BBUS using BB27 in a lot of their branding (Iirc their chronology has been slightly more consistent though) vs the recent seasons of BBUK using the year more prominently than BBUK20, BBUK21 and the upcoming BBUK22.
Anyway thats a bit of a tangent, But it sometimes happens also with scripted shows that get rebooted much later and such whether their new seasons fit in much with the original continuity, but back to BBAU even with Ch 9's three found myself going for referencing them 2012-2014 more often than BBAU9, 10 and 11 which I would use only occasionally sometimes depending on the context, perhaps the gap and newtork change making more of a distinction and breaking the pattern a little bit as well, as part of the 'BB (O)8' naming was in part attributable to the year of the 2000's too iykwim.
Even the hosts mainly use the year in the announcements as its much simpler for the GP when theres only one season airing per year 'Welcome to the first eviction night of BB2025!/ The Winner of BB2025 is,' etc. the technicalities are morseo for Wikipedia purposes et al (but the fans will know what season you're talking about! Haha)