Charles Morgan at CoinWeek.com has "done the math". There are far more ANA-Chicago slabbed gold Kennedy half dollars than were ever sold there - almost 500 more! Now think about this. NGC, the ANA's official third-party grader, required all ANA Inaugural Release slabbed gold Kennedy's (and the clads,too) to be accompanied by an original receipt proving purchase at the show floor US Mint booth. There was a code on all receipts proving the provenance. So we know that any show slabs from NGC had to be proven as to the source of the coin. PCGS had no such requirement. We do know that just short of 1,500 gold Kennedy's were sold at Rosemont. CoinWeek reports that NGC (again, with source proof) slabbed 1,136 of them and ANACS slabbed another 30 (also with source proof). That leaves a MAXIMUM POSSIBLE REMAINDER to have been slabbed by PCGS of 1500 - 1166 = 334, and that's only possible if all 1500 allocated were sold (they weren't), and ZERO went unslabbed (not nearly true).
For the past 15 years, I have kept track of prices realized from major auctions for Liberty Head nickels. For fun, I thought I would compare those graded by PCGS and NGC (with and without CAC stickers). I did this for grades MS65, MS66 and MS67. I started the run in 2008 as that was the earliest result that included a CAC sticker.