Probably time to call in the big guns! EDIT: What am I saying. They're probably sitting back reading this and watching us wrap yourselves around the axle on it.
These sort of hazy white milk spots are unfortunately very common. That one is more extensive than usual, and unfortunately placed over his face... but there is no known remedy for it. The suspected cause is due to an improper rinse of the planchet before it was struck. That means: the spot is struck into the coin (sorta like struck through grease). There is no way to remove it. There are 2 solutions for this problem: sell it, or melt it.
With your "really seems organic" I can only state that the Mint employee was eating a sandwich that had too much mayonnaise and when they took a bite the mayo dropped onto the coins. Lol
That coin is toast, unfortunately. I imagine some ASEs will look like this in 30-40 years. Fortunately, it wasn't a high value coin to start with.
Was this set purchased from the mint or post-market? I'm just asking because the cellophane packaging is fairly porous. It could have been caused, in part, by poor storage or contamination from a previous owner. The coin just hadn't turned yet.
direct from the mint, 60+ sets from the 60's and 70's were stored in a shoe box in various locations over the years
There are going to be a lot of really upset ASE / mint proof collectors in 30 or 40 years if this is what happens to those light milk spots.