Jerry and Kramer's apartment building address is said several times to be 129 West 81st Street, but the awning outside of the building has the address 757.
In some episodes, when exterior shots of the fictional "Monk's
Diner" are shown on two sides, you can see the real name, Tom's Restaurant.
Jerry's apartment number changes in the beginning of the series a few times before becoming 5A permanently.
The interior space of Jerry's apartment would be impossible given the exterior hallway leading to his apartment's entry door. His kitchen and the exterior hallway occupy the same space.
The exterior of Monk's Cafe does not match the interior of Monk's Cafe: the number and type of windows is different, the layout of the entrance is architecturally different.
In common with many other sitcoms, details of characters' back-histories change through the life of the series. We don't count these inconsistencies as goofs in long-running shows.
Looking through the bathroom door from the living room sometimes shows a bathtub against the far wall and sometimes a pedestal sink.