No, it didn't. I admit I don't know the history of zip codes in the US, but over here the postal codes weren't a thing until the 70s when the OCR devices were introduced: the idea was that you'd write a 6-digit postal code in the weird 9-segment font in the specific place where the machine would be able to scan it, and then sort and route it automatically. Of course quite quickly it turned out that people wrote wrong postal codes, or postal codes needed to be changed, so in the end the post service started filling those themselves, and they later started printing and sticking barcodes with internal routing information onto the letters, and using those.

> Getting a human to sort mail without looking up a big list was pretty useful.

Mail gets sorted several times. At the ingress, there is a rough sorting of "okay, this one leaves the city, this one doesn't" kind, where the former ones are thrown in a large bag and sent upstream, and the latter ones get divided into delivery groups — yes, by a person looking up a list of local addresses. They don't need to have a list for the whole country, only for their city/local district, so it's not that big of a list. And not making this list of internal routing codes public has the benefits that A) that number needn't be double-checked for correctness, saving the labour, B) the list can be changed often to better suit the way the delivery routes are organized, and you don't need to notify the general public about the changes.

I'd be willing to bet $50 that USPS has some internal DB, changed very often, that they use to remap zip codes into something actually useful for both the bulk- and last-mile delivery.