Perhaps there should be a term for a clue that can only be solved "backwards", by arriving at the answer from available letters and figuring the clue out from there. If this was a "free-standing" clue (the kind Jolan offers) I doubt that one could solve it.
Or is there such a term already? "Inverse" maybe? There's a term for the kind of murder mystery in which the reader knows who did it (and how) before the detective does. I think it might indeed be "inverse mystery".