An apotemnophiliac should perhaps more accurately be described as a person desiring amputation as a part of a sexual fantasy. The desired kind and level of amputation frequently change.
The problem is that these groups can overlap making the correct diagnosis difficult. Also there are other kinds of wannabes that have other objectives like becoming paraplegic.
The true wannabes are those who might benefit from amputation.
Note though that the current nomenclature probably will change in the future to more accurately describe the syndrome.