Re: Easy only if you know the answer
I agree with those above; the top number is the "official" number of registration, which is why you wouldn't see it installed at the factory. It is probably installed by the seller (broker or agent) after the paper work for registration is done. and the vessel then has an official number.
The second must be tonnage, as suggested above, as registered tonnage, be it net or gross, depending on the country of initial registration.
US boats have only the official number on the plate and by law that plate must be permanently attached (fiber glassed on or welded in the case of steel), not screwed on.
This number remains with the boat and does not change with ownership.
"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.