Then Wouter somebody had better call the Finn class and tell them that 3DL sails are ok to use without cutting and inserting seams as they currently do.

The rule in the Finn class (which is heavily scrutinised by sailmakers, sailors, federations and ISAF) clearly bans sails that have Continuous layers or fibres crossing the seams. If there were seams in a 3DL sail then they would in fact be legal for class use.

When you are finished theorising you can get back to reality and pull your head in.