This is standard on C&C rigging. Carriden has it, my 25 had it too. In essence, the copper swage is a marker to ensure the correct dihedral angle for the spreaders, so that they maintain the proper angle between the shroud and the mast. You may have noticed that when the mast is up and the rig is tensioned, the spreaders do not sit at an exact right angle to the mast. Rather, they are tilted slightly upwards, so that they bisect the angle formed by the stay as it inclines in towards the mast head. The copper swages are usually partnered with small washers and they get positioned immediately below the spreaders, when you are rigging the mast prior to putting it up.
In short, yes you should replicate the copper swages, in exactly the position on the shroud where they currently sit. When Bristol Marine replaced my one upper shroud, they made sure to include the swage.
Marcus from Carriden
Mk III, Hull #847