Wikipedia calls these "orphan initialisms", with a couple of citations (halfway down the page for Acronym): "an existing acronym is redefined as a non-acronymou

Wikipedia calls these "orphan initialisms", with a couple of citations (halfway down the page for Acronym): "an existing acronym is redefined as a non-acronymous name, severing its link to its previous meaning." But yours is catchier. Oh, I see they have "anacronym" too, with a fine distinction of meaning. It's the difference between the word officially ceasing to stand for anything, and the public generally forgetting the word stands for.