Yes there is a duplicate but I have never found any on three boats. This from WA state...
"Two identical hull identifcation numbers are required to be displayed on each boat hull. The characters of each hull identifcation number must be no less than 1/4 inch high.
Each hull identifcation number must be carved, burned, stamped, embossed, molded, bonded, or otherwise permanently affxed to the boat so that alteration, removal, or replacement would be obvious. If the number is on a separate plate, the plate must be fastened in such a manner that its removal would normally cause some scarring of or damage to the surrounding hull area. A hull identifcation number must not be attached to parts of the boat that are removable.
A. The primary hull identifcation number must be affxed as follows:
•.....
B. The duplicate hull identifcation number must be affxed in an unexposed location on the interior of the boat or beneath a ftting or item of hardware."