Other mistake: Magnum states his date of birth to the doctor; "August 8th, 1944." On his driver license in "Memories Are Forever" (when the General shows it to his wife) the date was January 5th 1946. (00:05:35 - 00:40:55)
Visible crew/equipment: When TC pushes Magnum's wheelchair while Rick and Higgins walk alongside, Higgins is relating the situation to another one of his experiences, and in the next shot as the Gilberts approach Magnum, a bit of the boom equipment is visible at the left side of the screen. (00:08:20)
Continuity mistake: The husband of Magnum's client shakes hands with everybody; in the first shot his other hand is at his belt, it's in his pocket in the following. (00:08:40)
Visible crew/equipment: When Tanaka escorts Magnum down the stairs in the guesthouse, just as Tanaka picks up a book from the coffee table and Magnum sits on the couch, the actor's white tape mark is visible on the floor at Tanaka's feet. (00:12:00)
Visible crew/equipment: When Tanaka asks Magnum if he's up to a little trip to jar his memory, in the next shot as Tanaka pulls up to the beach house, there's a black plastic T-mark on the sand beside the driver's side door. (00:14:00)
Visible crew/equipment: When Magnum and Tanaka are at the murder scene, Magnum says he remembers nothing about Joanie's murder (while having 'Nam flashbacks) so Tanaka tells him, "Strike two." It then cuts to Higgins and Magnum arguing about the car, and at the start of this shot lighting equipment is visible on the lawn, at the right side of the screen. There are also wood planks visible at the bottom of the screen, presumably used for the camera dolly to track forward. (00:16:05)
Other mistake: Higgins hypnotizes Magnum using as pendulum a medallion, which is a reused prop from the very previous episode; Paulo, the "travelling companion" aka boytoy of his ex fiancée, was wearing it in the finale. It makes no sense for him to have it - unless you want to write your own dark fanfiction about it. It was just a throwaway prop, on screen for a second or two, and reutilized for another brief scene here. (00:31:50 - 00:47:25)
Character mistake: Rick reveals Magnum that a certain person committed "security fraud." That'd be securitIES fraud. (00:40:20)
Continuity mistake: Dave drinks his glass almost reaching the end, but when Magnum pulls out of the gun, the glass at the edge of the table is half full. (00:43:00)
Continuity mistake: At the end of the episode, Tanaka approaches Magnum on the hammock and they have a chat. Sticking out from Tanaka's pocket, first his pair of glasses, then a packet of cigarettes for most close-ups, then the glasses again. (00:46:20)
Plot hole: Magnum gets through a wild goose chase because of two false clues, but their presence is not explained in the denouement nor makes sense. Magnum suffered no real amnesia, he says, and it's proven Magnum has never been to either places, so the parking ticket and card must come from the killer, linking them to the murder in an unnecessary way. They fill screen time nicely but do not fit the murder scheme.
Plot hole: The key plot point needs that the mechanics fixed a car completely wrecked in large parts of the chassis. So nobody gave it as much of a test run after working extensively on the aerodynamics, nobody sat on it for a moment, nobody drove it a few meters from the tow truck to the work area, at all and a single mechanic of the large car shop is able to say that with absolute certainty. It's an enormous stretch - not to mention that while Selleck's slouched posture in the episode makes it not entirely unbelievable, he is taller than Mark Withers by an inch, and the Ferrari was modified in real life to accommodate Selleck's size - there would be no way to push the seat further back, and the plot point is unnecessary for the resolution.
