It resembles Orthaga seminivea, except for the black area at the base of each forewing, and that species has previously not been found south of Newcastle,
Yes, O. seminivea seemed the most likely, but I've searched high and low online for a better match with so far no success. No obvious match for Australian or overseas Epipaschiinae on iNaturalist. Most similar was Teliphasa albifusa (white abdomen) but that was recorded in Hong Kong. The species is widespread in SE Asie. A 'blow-in'' due to this monsoonal weather perhaps?! .In private, museum collections or ANIC I wonder?
Yes, it's close to 0. seminivea put apparently different in a couple of respects. O. seminivea has been recorded in Wollongong and the nearby tablelands, putting it close to ACT, but it seems we need to keep looking.