It's honestly not that obvious. I never knew there's a difference between the 5-digit and 9-digit versions of my zip code. Most checkout flows do not even allow me to input more than 5 digits in the first place. But upon receiving my mail, the 5-digit code is always corrected to the 9-digit one.
I had never considered that if there were multiple 9-digit expansions of a 5-digit zip code, the correction might turn out wrong unless the full 9-digit code is specified.
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It's honestly not that obvious. I never knew there's a difference between the 5-digit and 9-digit versions of my zip code. Most checkout flows do not even allow me to input more than 5 digits in the first place. But upon receiving my mail, the 5-digit code is always corrected to the 9-digit one.
I had never considered that if there were multiple 9-digit expansions of a 5-digit zip code, the correction might turn out wrong unless the full 9-digit code is specified.