There was a program you could run on the TI calculators before clearing that did some voodoo magic so that you could memorize some short “binary” program that restored it all. My memory is vague but between clearing and executing this very short executable, it at least appeared to be completely wiped.
IIRC it was an applet that hooked the key shortcuts and menu entries for a wipe, and the really advanced ones would drop you into an imitation shell that appeared as a freshly wiped calculator would, but there was a magic keystroke to drop back to the (untouched) main system.
