Paddy, Happy belated birthday and thanks for posting the pictures and explanation of this underappreciated and scarce error type. I've never read what was different about the press configuration in the late 90's (when the vast majority were produced). Here's an absolutely terrible picture of the example in my set. It was filed under P for Paid Stupid Price. I'm a sucker for great examples of a single error type. I have never had the raw coin in my hand for precise measurement, but the fin here is, at least, as tall and the coin is thick Take care.....
And why am I being summoned? Finned to me applies to fish.........I've no knowledge to impart with regard to coins. [aside] (He buys his fish in the fish market. He can't abide fishing. He gets sea sick.)