the plot thickens - my green one has a rim like your plum one - heat finished, but with a sort of tiny lip ring around it, my neodynum one, has a rounded but absolutely straight rim. It's also smaller than the green one.
I'll get pics tomorrow - there's a 2mm thick layer of dust in them - and a collection of pins (how did they get there? :spls: ) which I very nearly tipped all over myself.
I had wondered Caithness, just a little bit, but I imagine the differences in rim finish would preclude them. I do see them around.