It was in 2014 that Birdlife International resurrected Gould’s Plumed Egret. This was followed five years later by Birdlife Australia in its WLAB v.3. According to the theory behind that, you only (or just about only) find Intermediate Egrets to Australia’s north. I know from bird hide conversations that this particular taxonomic update has been a surprisingly difficult pill to swallow. Even Birdlife Australia has difficulty with it. The Intermediate Egret A. intermedia is offered for ticking in the recent Aussie Bird Count. Australian Faunal Directory is also slow or unpersuaded. However, now that eBird and its associated taxonomy (Cornell Lab BoW) have accepted the return of plumifera the tide has surely turned, and I’d expect other lists to follow.
The real Intermediate Egret is listed as vagrant to Australia, but just how difficult will it be to add to your Australian list, maybe even retrospectively? It seems you’ll need to pay particular attention to those vaguely distinguishable bare parts. There is an intermedia/plumifera record for Christmas Island that will be due for revisiting, so check your diary or photo album for medium-sized egrets seen there. I see from the BARC archive that a claimed sighting of intermedia at Cairns in June 2019 is ‘under review’ (case number 1192).
Geoffrey