In the opening credits for the entire series, the type of luggage Felix is carrying changes.
When he is indoors (leaving his apartment or arriving at Oscar's) he is carrying a white suitcase. But when he is walking outside he is not carrying the white suitcase.
The apartment that Felix and Oscar share changes completely from the first few episodes. Since they don't move and the first is clearly larger than the later one, it's an error of continuity.
The opening narrator says Oscar was thrown out by his wife. The apartment he lives in is where he always was living. Blanche moved out and went to live with her parents in California.
In the opening narration, Nov. 13 is stated as the date when Felix was asked to leave his "place of residence." But no year is mentioned.
The scene of Oscar and Felix walking down the street talking to one another (that is shown at the end of the end credits) is recycled and clearly overdubbed with whatever conversation is appropriate to the episode.