I wasn't suggesting the gun might be out of proof. Rather, proof marks can tell you a lot. For example: was it reproofed for 70mm cartridges, was it reproofed for a larger internal diameter, was it originally proofed for black? It's just worth checking out and understanding the meaning of any marks.

Holland & Holland is the consummate authority on the Paradox guns and nothing could be lost by letting them have a look at it. The last Paradox gun I purchased, I had the seller take it to H&H and made the sale conditional on a clean bill of health. It was understood that H&H wasn't required to verify that the gun was pristine or in the condition they would require to sell themselves. H&H was only to to verify the gun was in sound working condition with no major or hidden faults. They let me know every little thing about the gun and made recommendations on work should I purchase the gun. In the end, I made the purchase and had the gun delivered to H&H for some of the recommended work and for import to the USA. Because the buyer, the seller, and the gun are in H&H's backyard, it seems like a prudent course of action to me.