I usually place the most weight on actual sales even the prices may be no where near what price guides say. Looking at Heritage's archives and
ebay, the ones in NGC holders sold in roughly the same price range. It's only the ones in PCGS holders that hammered above $200. I think the population totals and set registry are a factor in the price difference. NGC has graded 156 in and another 12 in 67. PCGS has graded 59 in 66 with the highest being a lone example in 66+. For someone building a NGC registry set, they can increase their score and possibly ranking by getting one of the ones in 67 instead of in 66. PCGS registry set builders are not left with too many options; they most likely have to settle for one of the 59 examples since I think the 66+ is probably in strong hands.