In "The Sport of Kings," Sub-Inspector Singh testifies the blood found in the car was "O-Negative." The term 'negative' refers to the Rh D factor, which was not discovered until 1937 but the series is set in the early 1930s before that discovery was made. Prior to 1937, only the ABO blood group system was known; so the line should have just stated the blood type was "O."
The series rakes place in the 1930s but the local constables carry No4 Mk1 Enfields, which were introduced in WWII, ten years later.
Superintendent Tyburn quits the Kenya police when Commissioner Burkitt forces him to charge an innocent man. However, in episode 1, "Private Lives," it is established that Tyburn is working in Africa because his other alternative is an English prison. In fact, when asked if he's staying on as Superintendent, he tells Emma Fitzgerald that he has no choice.