The analyzer only takes into account items taken from inside creatures bodies.
a few months ago it was possible to put items inside dead creatures, so you could put a mastermind shield inside, then put back into your backpack and the analyzer would say you looted +50,000 gps.
When you un rust something, you will most likely be doing it from inside your own backpack (after looting the rust armor), so the analyzer will just add the value from the rust armor and not consider the value of the resulting item.
A way to maybe go around it, is to un rust the item BEFORE looting it, so when you actually loot it will be a knight armor, instead of a rust armor, for an example. I haven't tested it yet so I can't guarantee that it works, but I'm 90% it would.