One thing that boggles my mind is how the 1899P Morgan dollar doesn't command a monster premium in lower uncirculated grades even though the official mintage was only 330,000 coins minted. Yeah yeah, I've read that some try to paint an image that in 1900 they minted more with the same dies but Stacks and Bowers says probably not. Then there is the Pittman Act that probably destroyed half of those. I have 4 of them from AU53 through MS62, but it's absurd with that low a mintage they do not command a serious price for them, as compared to 1899S which had 8 times more coins minted. Another mystery!
I don't really have a good answer but I believe this was one of those years that a lot of bags came out in the 50s and 60s. Maybe that kept the price down?
Bowers Red Book says that while the mintage total may be in doubt (?), there were bags of 1899's released in the 1950's and in the West in 1962. 50,000-100,000 may have been released. While lots of MSD collectors are around, that is a decent supply to satiate demand. Obviously, if Mint State coins are plentiful, no need to bid up AUs.