I thought they just hadn't been updated as the population had grown and the road status had changed from various major/arterial levels as there seemed to be a lot of tertiary roads but not many secondary. I checked the Australian tagging convention but didn't see anything that defined the levels, I only went to change a local road I noticed but then went down a rabbit hole and changed quite a few.

How would OSM correlate to the categories of road defined by VicRoads? It's seems to be close but not quite the same.