At the beginning reference is made to the arrest of D S Morse from the last series, in fact he was D C Morse.
When DI Thursday examines the murder victim's purse contents he flips through an address book which clearly has blank spaces for fax machine numbers near each entry.
Despite taking place in 1967, a character is introduced as having earlier won a trophy at the French Open. The French Championships were held until 1967, and did not become known as the French Open until 1968.
At 4 minutes 57 seconds, when Anthony Donn offers Endeavour a lift, his car has a rear view mirror suspended from the windscreen head rail as it would be in the majority of modern cars; at 6 minutes 29 when the two are talking in the car the mirror has disappeared; at 7 minutes 26 seconds when they meet Anthony's horse riding relative, the rear view mirror has reappeared.
When Anthony Donn is driving Morse through the woods and they are halted by police, Morse tells him to "take a left" for a short-cut, so that he can avoid being seen by Thursday and Jakes. This Americanism is not common in British speech even now, and would certainly not have been used by an educated Englishman in early 1967, when this story is set. He would simply have said "Turn left".