The nand gate fix wasn't to fix a bug in MTPI but rather to allow access to the
user-I from the program itself, primarily to make the *abomination* nargs() function
work.
I don't believe DEC ever worried about "fixing" this as none of the DEC
OS's and not even the stock UNIXes could even implement such a problem. You could
chew up some processor time, but you couldn't absolutely lock things out.