look at the edges of the slug. If they are smooth, as the edges of the finished chip are, it has likely been recovered from a completed chip. If the edges are rough (as cast), the slug has not yet been through the molding and machining process and is raw material for chip manufacture.

There are not many of these around. I would guess less than a hundred or so from all the various PMSC chips that were made. They sometimes sell for only a few dollars, but for someone interested in chip history, adding a new one to his collection might cost as much as $50-100. I have only a handfull in my collection to date. Harrahs seem to be the easiest to find.