Thank you all for the information so far. Very mysterious. The Trewenneck's (sp?)
arrived in Adelaide in 1852. There was a brother, Henry and his sister Elizabeth, both of whom came with spouses and families. It gets really interesting with Elizabeth being married to her first cousin John Henry.
Plain Henry was a blacksmith and John Henry was a potter. They all had lots of children, some of whom intermarried with their cousins and also married other Cornish families in SA, Orchards, Landaff Mathews, Bice, Pappin and Purton. The Caddy name pops up at least 3 times as a middle name for boys in both Plain Henry and John Henry's children.
I am still curious to know where it came from? One of the Mothers' mothers perhaps?