Skunkerama...
If I had found a fully built piano (or parts thereof), on board and not listed as official freight (manifested) then its off.....! Followed by an incident report....
Given that I suspect that the second piano was stripped down and therefore probably hidden among the closed containers, then there is not much that could be done. All the freight was check weighed by movers, so no issues regarding load weight on the trim, which would have been my main concern.
I don't want to be a party pooper, but with a little forethought, contacting the det location ahead of arrival, and getting them to advertise for a cheap upright in their local rag, would probably achieve the same result without all the hassle.