Leather Cuirass Lorica Musculata, I used to think no way but

[Tarbicus]

The fact is the sculptures do appear to show a stiffened but flexible garment. Whenever the wearer is slightly cantered or bent the garment always bends with them; metal does not bend like that.

But an effective leather armour wouldn't bend, as Dan Howard has often pointed out. I think you also ignored my comment that you can't trust a paid artist to truthfully represent a cuirass if it conflicts with the pose of the actual subject, the wearer.

The officer’s knot always appears to pull on the garment and the garment usually appears to have a leather lace up at least one side, with a tied knot at the top under the arm pit. There is no aesthetic reason for the artist to add a leather lace with a bow tie under the arm pit. Many show leather hinges as pointed out by Travis, not metal hinges.

Segs are held together by leather strips, they articulate X times more than a musculata, and they take a while to break.

I have a leather musculata (shock) and when tied by a Knot of Hercules it doesn't pull on the garment, it just helps keep the halves in place. The same would apply to a metal cuirass. Soooooo, if the halves are tied with leather thong, what better than a little extra guarantee?