Metal plate beneath Linothorakes or Spolades

[Dan Howard]

One more thing springs to mind--if this particular piece of bronze was made to go inside something leather or linen, presumably riveted in, why go to the effort of riveting 2 pieces together first?? Why not just rivet or lace them in place individually?

This is the main reason. The suggested construction is impractical and counterproductive. Real armour was riveted directly to the foundation to improve articulation. You won't find an example anywhere where the plates are riveted to each other unless there is no foundation involved. So, assuming the plates in question actually come from body armour, it is unlikely that a "coat of plates" type foundation is involved. In other words, if these plates come from body armour then there is no leather or cloth cover involved.