The reason I leaned the way I did was considering items that "prevent all sanity loss from one source." If ALL truly is ALL, then this item will not work. If it does work, then it implies that it blocked a number, so there's a number to be associated with the loss. If Harvey has 5 sanity, then ALL means 5; it can't mean 6.
But, I'm open to the idea that this loss is not preventable.
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