Every Sandman I ever saw new back then had them fitted, it was a very rare set of GTS wheels that didn't have trim rings whether it was a Sandman, Monaro or whatever. The only new car I remember seeing without them was the L34 and A9X Torana. Both of them were stripped down bare essential cars, so trim rings didn't get a look-in.

So anyway, even if they weren't "factory" standard, they were fitted anyway just because the wheel looked finished with them on.