It’s not a stomacher. It’s two of the cluster brooches one above each other with one of the two larger pendants and two of the four smaller pendants arranged in formation. I’m not sure if anything other than the tiara was sold. My guess is that all the clusters were called into service to get enough elements. The necklace, brooches, earrings and pendants are now a necklace, Tiara, earrings, pendants and at least one Brooch.
https://pin.it/3ofjse6bz3bmk6