Spoke to a very helpful woman at the AEC and it turns out Holly and I are enrolled to vote, just not at the address we expected. I'm sure we enrolled and registered as overseas voters from my parents' address, but it turns out we're enrolled at our old place in Stanmore. This probably means that all our previous votes were discarded.
The good news, however, is it means our votes are a bit more use in lower house elections. At my parents' place, it's super-safe Liberal whereas Stanmore (Grayndler) is somewhat less safe Labor.