To answer your question, the first thing to remember is unlike the book “Animal Farm”; not all grading companies are equal. In my experience over the years, we have sent into PCGS way more than fifty NGC graded Kennedy half dollars for cross over and they have almost always lost 1 – 2 point each (maybe three crossed grade for grade). As a general rule when buying NGC coins, we take the different grading standard into account and adjust accordingly, in other words we will offer or be willing to pay PCGS price of a MS67 coin for a NGC coin graded MS68. Not sure if I qualify as a “serious collector” of Kennedy half dollars but I have a copy of Rick Tomaska’s book on Franklin and Kennedy Half Dollars and I would not recommend any collector of the series to buy this book – it is useless. The only books on the Kennedy series I would recommend is the current edition of the Red Book (for mintages) and the second book I would recommend even that it is outdated is James Wiles’ book “The Kennedy Half Dollar Book, An Attribution and Pricing Guide”.