For the moment, I'm going with Mount Buller which covers Mount Stirling. If I get time and interest I'll look into what I can source. My challenge will be misaligned data from multiple datasets.
I very strongly suspect that the data used for almost all sources is the ABS data. The unincorporated areas are not subject to ABS data collection and analysis. The fact that Mount Buller and Mount Stirling are conjoined in the ABS data implies, to me at least, they they have no boundary between them, because they aren't interested in them. The other unincorporated areas are all separate and would leave "donut holes" in the polys and so get calculated that way. With the two joined at the hip, as it were, no separation needed
