Excellent job with those beautiful little silvers. Here in the US we love getting our tiny Trimes and 1/2 dimes. Definitely a sense of accomplishment when we do get them.
Strangely enough, yesterday I had a hunt (here in Maine, USA) along a wet, rocky saltwater shoreline and I also pulled out a 1919 threepence. Coming from literally under rocks in salt water it is not in as good shape as your little babies. It even had a cup to it. Definitely a big surprise though.
The 6 inch coil on the Equinox did a very good job. It came in loud and clear in beach2.
I'm wondering what the difference in your Australian three pence and the UK three pence is? The front of my coin looks to be just like your 1917 on the top right. I'll try to post both sides of this coin when I get it cleaned up.
Thanks very much for your help and good luck when you get back out in the field.