On the second disc in the HARDY set, Leonard Maltin does another introduction (different from the one on the first disc), and in it, he mentions that there WAS a second Hardy mystery - THE MYSTERY OF GHOST FARM.
I thought I remembered a second Hardy mystery from THE MICKEY MOUSE CLUB, but in talking with someone yesterday about it, I talked myself out of it saying that maybe I was confusing it with the second SPIN & MARTY serial.
Anyway, I'm hoping Disney will release this one in another year or so. I'd love to have both of them.