Sometime ago, it was reported some undocumented opcodes like GO->XQ, ?OFF, POWON, ?WKUP, KEYS=C that are supposed to be used in the HP-41 internal Master Control Program. For instance, a description is found in the english edition of J-D Dodin's book "Inside the HP-41".
Having received my Datafile archive CD from Jake Schwartz a few days ago, I came accross the original description of these instructions as published in Datafile V3N2p15 under the "April Column" by Bill Reggusy, who was supposed to have made his discovery on his HP-41C SN 2321S010484 (!).
Do you see now where I want to come to?
Actually Bill Reggusy wrote a small note in Datafile later to make clear for everybody that it was just a hoax. The funny thing is that it this hoax was seriously reproduced in a book, and maybe in some other publications.
I must admit I thought to support these opcodes in my Emu41...
J-F