No, as posted above, it's #4...the 1921. The 1927-D went from a Top 10 or so rarity to ultra-rare to the rarest in about a decade's time. The dealers and collectors believed there were a few dozen out there when in fact it was only about 1 dozen or less.
I think in that circumstance it is TOTAL population and not MS-64 or Gem population driving the price. Good observation though, Charley....with fewer high-end examples the 1921 sells for LESS than the 1927-D, even in the same high-grade. Interesting....
The 1921 had a coin sell for just over $2 MM, but it was that proof specimen claiming unique status: https://coins.ha.com/itm/saint-gaud...3-3499.s?ic4=ListView-ShortDescription-071515 The 1927-D Duckor Saint sold at FUN 2020 (I was there) was only MS-65+ and went for a bit higher price, also just over $2 MM. The next highest 1921 was just over $1 MM so I think saying that in high-grade the 1927-D is the priciest Saint is correct.