Hi @SenexRugosus , you have recorded that there were between 4 and 15 plants, were all of them pure yellow? The flower doesn't really look like D amabilis.
Yes, they are all pure yellow. There is a a colony of sulphurea about 10 metres away, all with typical sulphurea coloration. I can take more photos of particular features if that would help the ID.
Thanks @SenexRugosus . I agree with Matt that is likely a yellow form of D. sulphurea. D sulphurea can reproduce vegetatively so the resulting daughter tubers/plants would also exhibit the same colouration as the parent plant. A characteristic of D sulphurea is that the callus on the midlobe has a single ridge, I think that is what I am seeing in most of your photos.