Episode #9.2 - S9-E2
Revealing mistake: Rose's newborn baby, Isabel, is suspiciously large and mature.
Grantchester (2014)
1 revealing mistake in Episode #9.2
Starring: James Norton, Morven Christie, Robson Green, Tessa Peake-Jones
Episode #1.3 - S1-E3
Other mistake: The publican asks for payment for some drinks, saying "One and six, please", meaning one shilling and sixpence. The subtitles say "One-o-six, please."
Episode #7.5 - S7-E5
Trivia: The Matron is called Fletcher. Louise Fletcher played the chief nurse (and a similar character) in "One Flew Over the Cuckoo's Nest."