It can be tough to tell from images, but while the font in the overprint on the stamp in question is similar to the others shown, it's also bolder with thicker stems and serifs. Possible fake overprint?
At one time, the PF relied on outside experts. Many of those no longer live or walk in the PF. Perhaps they should rely on outside experts more than they do, if they are doing so at all. Will you alert them to correct the error? We're all human and make mistakes.
The stamp in question sold today at Siegel for $550 + BP with no mention of the fake overprint.
Like an idiot, I actually was the underbidder. I completely forgot about this discussion. Bart mentioned the fake overprint in a subsequent email conversation we were having during the session, which jogged my memory.
The PF cert # mentioned in the OP has been removed from the PF website. I hope that Siegel will contact the winning bidder or that the buyer put it on extension.
Overall, the bidding was quite lively today. I was surprised at how well the wine stamps did, as those typically don't see a lot of activity, comparatively speaking.
I got shut out both yesterday and today, with the exception of one lot, which was actually the lot I wanted most from the 2 days, and it actually went fairly cheap... go figure.
Where can I find a listing of the serial numbers printed for these and stock transfer issues etc. Thanks !! I find overprinted issues in old auction lots and question the serial numbers quite often as fakes.