I'll admit to never quite understanding all of how the USPS defines "town" and maps their Zone Improvement Plan Code areas. But I've seen a few oddities.
When I lived in Illinois prior to getting married, I lived most of the time in Palatine. Palatine shared its ZIP code with neighbor Inverness. Inverness is much smaller than Palatine, but is also much more well to do. So as far as the USPS was concerned "Inverness" was the secondary city to "Palatine" for addresses to that ZIP code. But many shippers and bulk mailers would automatically substitute "Inverness" for "Palatine."
Then, not to far from where I work is a large neighborhood entirely contained within the city of San Diego. But any of the zip codes assigned to that area the preferred, and possibly only, city that is allowed is "La Jolla." I'm not 100% sure when San Diego annexed the La Jolla area - although Greg Binford used the annexation of La Jolla and a renaming of the local branch of the University of California as a time point during the 1961 or 1962 parts of Timescape (I think that is the name).
Of course sometimes it is people who get weird ideas about this, which don't pass basic sanity. I had a friend through college who lived on a short road in a neighborhood that shared its ZIP code with where we lived in Alameda (NM). The road he lived on was Academy, which was also the name of a much larger road in a different quadrant of Albuquerque (NE instead of NW) and never entered our ZIP code. But he remained convinced for as long as he lived there that if any mail was addressed to the city of "Albuquerque", the post office would deliver it to the wrong address, but if they used "Alameda" it would work. Where we lived, which was in the area considered Alameda, we always used "Albuquerque" on our addresses (and my parents still do).
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When I lived in Illinois prior to getting married, I lived most of the time in Palatine. Palatine shared its ZIP code with neighbor Inverness. Inverness is much smaller than Palatine, but is also much more well to do. So as far as the USPS was concerned "Inverness" was the secondary city to "Palatine" for addresses to that ZIP code. But many shippers and bulk mailers would automatically substitute "Inverness" for "Palatine."
Then, not to far from where I work is a large neighborhood entirely contained within the city of San Diego. But any of the zip codes assigned to that area the preferred, and possibly only, city that is allowed is "La Jolla." I'm not 100% sure when San Diego annexed the La Jolla area - although Greg Binford used the annexation of La Jolla and a renaming of the local branch of the University of California as a time point during the 1961 or 1962 parts of Timescape (I think that is the name).
Of course sometimes it is people who get weird ideas about this, which don't pass basic sanity. I had a friend through college who lived on a short road in a neighborhood that shared its ZIP code with where we lived in Alameda (NM). The road he lived on was Academy, which was also the name of a much larger road in a different quadrant of Albuquerque (NE instead of NW) and never entered our ZIP code. But he remained convinced for as long as he lived there that if any mail was addressed to the city of "Albuquerque", the post office would deliver it to the wrong address, but if they used "Alameda" it would work. Where we lived, which was in the area considered Alameda, we always used "Albuquerque" on our addresses (and my parents still do).