Regarding plans, the majority of plans that are 100, 200, and 300 years old are shrunk, stretched, taped, or otherwise not like the original. If I redraw the plans, tracing them does not work perfectly but can be modified so no one can say it is a copy. Also, using the appropriate contract or chart of scantlings when a contract is not available, dimensions can be fixed if they are not correct. With CAD, the drawings should be more exact than hand drawn. Based on the contract the gun deck beams on Agamemnon were sided 15.25" The drawing has them at 18" and as they are hand drawn, vary. (They are even smaller in the scantlings from the Shipbuilder's Repository 1788 and The Elements and Practice of Naval Architecture.)
There is fold/crease in the middle of the plan so the over length is off as well. At our scales, who will notice? The point is, if the plans have mistakes and they are redrawn because the contemporary plans have changed over time, would there still be a copyright issue unless the redrawn plan has the same mistakes.