[a fool in paradise]

While they may have been “looted” or given out as gifts by the publisher over the years, as with other stolen property, when it comes up at auction, it could still revert to the estate.

[denydenydeny]

The best article on the theft of Kirby's art by former Marvel staffers is here. The originals, unfortunately for the Kirby estate, are a bit of a legal grey area since it was all work done for hire and other companies of the day (DC for example) routinely destroyed the originals.