Misdialling short numbers on a rotary phone was easy and common. If your finger slipped out of the dial it would return at that point and dial a shorter (lower)

Misdialling short numbers on a rotary phone was easy and common. If your finger slipped out of the dial it would return at that point and dial a shorter (lower) number. The most common point for a finger to slip was at the start of each turn, so if your finger slipped you would mostly dial ones or twos. You cannot dial a 9 in this way. The amount of time it took to dial 999 was inconsequential. Nothing was instant in the days when this protocol was invented.