Morse admits to having difficulty in pronouncing Welsh words and names and refers to Ifan Roberts as "Iff-an", and his daughter Siwan as "See-wan"; the names should be pronounced as "Ee-van" and "Shoo-an", respectively.
When Morse is found watching a blue film (for work purposes) by his stepmother, he alludes to "Reveille", the cheap British pin-up magazine of the 1940s which was, by the early 70s, containing photos of actually naked, rather than simply scantily-clad, girls. But Shaun Evans mispronounces the name of the magazine as "Re-Vail", rather than "Re-Valley".
The number plate of the first taxi shown is RAR 540L. This was registered between 1 August 1972 and 31 July 1973. However, this series is based in 1971. So, the car wouldn't have been on the road in 1971.