In a majority of season one and season two episodes, location/establisher footage showed Jane Hathaway's first car, a 1962 Plymouth convertible, but in some cases the scene would immediate cut to a close up of her arriving in a 1963 or 1964 Dodge.
The long shots of the mansion in the closing credits show no benches on either side of the front door. In the closeups of the Clampetts coming outside, they are there.
During the Closing Credits of season one's Thanksgiving episode, immediate link: Elly's First Date (1962), a grounds keeper is clearly and easily visible, walking towards a filming camera on the right side. He is carrying a rake and wearing a white armless (tank-top) shirt. He abruptly changes his path and looks deeply shocked, when he realized he was accidentally being filmed, apparently. He then immediately ran off the film of the camera screen, to the right of the film screen.
During the closing credits of Pygmalion and Elly (1962), shows a man's right arm (with short sleeved shirt) as he is walking on the driveway toward the camera, and then it/he is jerked out of the picture as he gets close to the camera.
The premise of the series, according to the pilot & the theme song, is that "a poor mountaineer" accidentally found oil on his property. But oil deposits do not occur in or near mountains - the geology of a mountain does not sustain oil pockets.