Plot hole: In the first season, Lucy Ewing had an affair with Ray, the farm hand at South Fork. Several years later, it was revealed that Ray was actually Jock Ewing's illegitimate son, making him Lucy's uncle. However, the subject of their affair was never raised, even though they surely would have been at least somewhat traumatized upon learning of the accidental incest.
Plot hole: Michelle and the girls are winning at Baccarat every time due to a system where they know the cards in advance by seeing through them. However, all betting in that game is done before cards start coming out of the dealer's card chute onto the table. So even with their cheating system, they realistically couldn't always win, as the cards are not already face down on the table.