Dave-
One thing that is strange: why would Purdey sue anyone? I believe Purdey's rights to the Beesley patent expired long, long ago, probably well before WW1
If that's the case, it can be copied by anyone who wants to gear up and do it. I've been told that no one makes gun on the Beesley action because it's too difficult and expensive to do. And I'm not sure there's any advantage to it, either. While it's an interesting action, I don't thing it has any real benefits.
I would love to learn anything more about the Defourny-patent self openers. Do the guys on that board you mention have any more info?
And I bet the gun in question was made in Belgium and then brought into Spain. I don't see why anyone would smuggle it in, or do anything like that. As far as I know, there are no laws against bringing a gun in from one European country for sale in another. The Spanish proof marks were probably added by the Spanish "maker" to make the gun look Spanish.
Thanks
OWD