How can you test that a palace was stored correctly?

Walk it backwards, or jump to a random locus — if the images are solidly placed, order and content survive both.

Because a palace gives random access, you can probe it: recite the items in reverse (walk the route the other way), or ask "what's at the 4th locus?" and jump straight there. Robust storage passes both tests; if reverse or random access is shaky, some images are weakly bound and need re-staging. This doubles as a review method — the harder retrieval strengthens the memory more.