Hi Maureen this is what Derek replied: “There may be some coincidence in this. Some years ago I was briefly in contact with a lady who was researching the ‘Prosser’ name, so was looking for possible relatives, and I think there was a Kalgoorlie connection.
I mentioned to her that we would probably be related way back, as I believe all Prossers come from the one locality in Wales. The name was apparently originally Rosher, then ApRosher; (from or son of); the ‘A’ fell off, so here we are today. There is a story that Rosher/Rosser derives from Roger, the original Welsh language not having a hard ‘G’. I passed all this on, and think she said a relative was Thomas(?) Evan Prosser, which seemed to indicate a Welsh connection.

I will ask him Maureen