Double Dukes - S4-E2
Continuity mistake: If you look closely during the first scene where Turk and Moody (disguised as Bo and Luke) reveal to Roscoe that they aren't Bo and Luke, as they peel off their faces. First Moody (as Luke) is wearing a solid light-blue shirt. When we get a close-up of his face, he is wearing Luke's traditional blue-pladed shirt, and after their masks are totally off, Moody is wearing the solid light-blue shirt again.
10 Million Dollar Sheriff (1) - S4-E8
Continuity mistake: In the first scene that Steele is chasing the Dukes in, he hits the side of the General Lee. You can see that the side is badly damaged. But in the next shot when the General Lee is taking a sharp turn and sliding, you can see that the car is repaired.
Dear Diary - S4-E20
Continuity mistake: While it's forgiven that the Generals usually have subtle changes through episodes and the series, in this episode we see a General with extremely inconsistent graphics when Bo and Luke deliver the counterfeit money to Winston. The 0 is off and the bottom of the 1 is extremely long.
Answer: Various reasons, but mainly to drive the Dukes out of Hazzard County because the family have been foiling his schemes since his and Uncle Jesse's bootlegging days.
Captain Defenestrator