There has never been a shortage of blast white Morgans. Those who can remember in the 1950's and 60's at coin shows and shops, few colorfully toned coins, silver was either white or grey dirt, with a small number from National Coin albums or paper envelopes that had color. By the 1970's some collectors were intentionally toning coins in kraft envelopes and many other methods, which expanded in coming decades. Now you see cases of toners at shows with all kinds of colorful tarnish, IMO most are intentionally toned. There is no clear definition of AT/NT - it is all tarnish, which is corrosion. So the collecting world uses words such as toning and patina that sound much better than labeling an item as corroded. Collectors pay huge premiums for the right tarnish- which feeds the AT doctors.
I am troubled by the marks in the field. Unless the reverse is absolutely pristine. It stays in the 66 camp for me.
I wonder what percentage of toned coins that go to NGC and PSGS are given a grade and what percentage are deemed “questionable color,” if such stats are kept. That info might shed some light on Kurt’s points.