What is the difference between a generic CEP and a street CEP?
A generic CEP covers an entire town or a broad area with no registered street address, usually ending in -000; a street CEP points to a specific street or a stretch of it, with a neighborhood and sometimes a numbering range set by Correios.
Why does the same avenue have more than one CEP?
Because the 3-digit suffix identifies a numbering range, not the whole street; long streets in capital cities get several CEPs along their length, one for each stretch that Correios sorts separately.
Does a P.O. box CEP work to find someone's home address?
No. A P.O. box CEP is tied to the Correios branch that manages that box, not to the holder's physical address; looking it up returns the branch's data, not a home or a company address.
Does a CEP's leading digit always map to a single state?
Not necessarily: the ten-region split groups more than one state under the same leading digit in several ranges, so two neighboring states can share the same first digit while the rest of the CEP separates the sub-regions.