Mr. Drucker state that Hooterville's zip code is 40516 and 1/2. However, in season 4 of the television series, he states that their zip code is 3.
The outside layout of the Douglas' house changed, but the inside layout remained the same.
On the original series, the railroad ran directly next to Drucker's Store. In Return to Green Acres, the railroad is gone. Since Hooterville has always been "behind in the times" and is not much keen on change, it can be assume the store was never relocated and the railroad was never dismantled.
At the Douglas' going away party, the songs the band plays have a drum beat, but no drummer onstage.