There's a linked thread somewhere that describes the operator console. It mentions the buttons were laid out in a linear fashion (vs how they were displayed on the screen), which in my mind is why they wanted contestants to call one number at a time - the operator needed time to find and push the button to reveal, then clear. G/T were pretty copious with their rules. I would wager there was a rule or criteria they hung their 'close' bonus win/lose decisions on.