Now, that, is technology.
https://www.usps.com/zip4/
After you enter an address, it's under "Mailing Industry Details", shown as "eLOT" (not sure what it stands for)
https://ribbs.usps.gov/index.cfm?page=elot
The mailman gives the next stack to each house in turn, and apparently didn't notice the address was off.
In my case it always happened when it wasn't my regular mailman.
https://www.usps.com/zip4/
After you enter an address, it's under "Mailing Industry Details", shown as "eLOT" (not sure what it stands for)
https://ribbs.usps.gov/index.cfm?page=elot