Cabbage Whites have the black dots on upper wings and underside forewing. Your images are of the hind wing underside. Hind wing underside ground colour for the Cabbage White is described as 'yellow weakly suffused with black' (Michael F. Braby, Butterflies of Australia Vol 1 p 343 CSIRO Publishing 2000). For underside image comparison between the two species refer: Cabbage White: https://bie.ala.org.au/species/https://biodiversity.org.au/afd/taxa/934ecab5-798d-45b9-bade-16b3380d08a0#gallery For Lemon Migrant: https://bie.ala.org.au/species/https://biodiversity.org.au/afd/taxa/b778fe7d-3677-4402-a955-a60ca435540c#gallery
Thank you so much for the links! From the photos in the suzi bond book and a cursory google image search my photos looked very similar to or essentially identical depending on which phototo the yellow migrant. But with digital copies and a broad range of images to draw on I can actually understand exactly what you are talking about and see the particular details that make this a cabbage white.