I think it's uniformity. You have 9(n) all over the place, and only pay attention to the number in parentheses. It's more error-prone to count repeating charact

I think it's uniformity. You have 9(n) all over the place, and only pay attention to the number in parentheses. It's more error-prone to count repeating characters, and it's easier (to me) to notice a typo in the form 9(4) instead of 9(3) than 9999 instead of 999.