In some early episodes, McGarrett leaves headquarters in a 1967 Mercury 2-door sedan, and reaches his destination in a 1968 Mercury 4-door sedan.
After the original 1968 Mercury was replaced with a 1974 Marquis Brougham 4-door hardtop, some stock footage shows the 1968 Mercury passing or in traffic.
In the opening title sequence, a hand loads a .38 snub nosed revolver, then spins the cartridge. The gun is loaded with bullets that have already been fired. The depression where the firing pin strikes the cartridge is clearly visible on all of the shells loaded.
In the now-famous scene from the opening credits, Jack Lord is shown from a helicopter shot on a balcony atop the Ilikai Hotel, then turns to the interior of the suite. The scene cuts to an interior shot making it appear that he turns directly from the balcony to face the camera after the cut. Actually, based on the scenery behind him, the interior shot had to have been made in a suite on the opposite side of the hotel.
In the closing title "outrigger" footage, the curved edge of the camera lens housing is visible in the corner of the screen in one shot.