Iver Johnson with strange stamps

[frenchie1]

I'm sure someone here could help me with this Iver Johnson in 38.
I've made some research on the web about this gun, but no one seem to have the same stamps than mine, so i need help to identify it.

 

[Jim Watson]

The barrel stamps are British proof marks.
I don't know enough about IJs to think serial number and patent dates unusual.

 

[frenchie1]

BNP means Birmingham Nitro Proof, but this stamp is in use since only 1954. I think this gun is much older but i don't know the year of manufacturing.
It seems to be a third model, but the patent is aug 25 96 only. I saw everywhere that the third model has different patent.
That's why i try to know more about this gun history.