When Juliet begins reading her Bronte book, Isola looks at the clock and it says 8:00. When Isola turns off the alarm the clock still says 8:00. After Juliet eats the potato pie the clock is sitting on a table and it still reads 8:00.
Kit's hair accessory turns from a small hair bow to a barrette during the same scene when talking with Juliet.
In Juliet's room immediately after her return from Guernsey, Sidney takes off his glasses to kneel down beside her and convince her to write about the Society. In the next shot, filmed from a different angle but continuing the conversation, he has his glasses on.
At about 7:58 Juliet and Sidney are walking from left to right After leaving the flat that Juliet does not want to buy. A woman is seen walking in the opposite direction pushing a pram. She approaches quite closely but she is not seen passing Juliet and Sidney.
Between 1:15:30 and 1:16:20 when walking from Ms Stimple's place to Isola's house, Juliet's shirt buttons change from large to small and back again.
The C-47 aircraft is painted with D-Day Invasion Stripes. These were removed from aircraft by the end of 1944.
When the parcel containing the manuscript of The Guernsey Literary and Potato Peel Pie Society arrives in Guernsey, it is labeled "OHMS". This stands for "On His (Her) Majesty's Service" and is only used for mail sent from UK Government Departments. Since the parcel was posted by Juliet Aston, it would not have been labeled OHMS.
Early in the movie, German Wehrmacht (Army) soldiers are operating a truck with a swastika emblem on the door. Guernsey was occupied by regular Wehrmacht troops (319 Infantry Division), so vehicles would have been emblazoned with the Iron Cross. The swastika markings were mainly used by Waffen SS units, which were not posted on the Channel Islands during occupation.
When poring over the archived Guernsey papers there is an article where an incident it is stated as taken place in St. Peter's Port. The correct name is St.Peter Port, not the sort of mistake a local paper would make. In Guernsey that is something over which the inhabitants of the island are sensitive.
Characters repeatedly refer to "The London Times". As it is the first and oldest 'Times' newspaper, the London publication is simply called and referred to as "The Times". Later versions from other cities (e.g.. "The New York Times") have the city name attached, but in the United Kingdom and Channel Islands the London paper would be called "The Times".
The medal given to the young boy during the evacuation scene is revealed to be a silver plated copy, the props department got carried away with the aging process rubbing some of the silver plate off revealing the copper core beneath. A real Military Medal, MM, is solid silver not silver plated.
In the beginning Dawsey states that the German's took all their animals in 1940. Later, when he meets Christian, he speaks of a cow giving birth in 1941. If all the animals were confiscated, that would not be possible.
When Juliet arrives at the club meeting, at dusk, some chickens walk around her. At that hour they should be sleeping.
When the couple are taking off in the airplane the seat belt has Nov 59 printed, presumably November 1959.
When the prospective Literary Society members ransack a derelict bookshop / library for their reading matter, the stock seems relatively undamaged by rain despite the fact that the wrecked / bombed building would have been open to the elements and also perhaps have been drenched when putting the fire out. Also, any books in salvageable condition would have surely been rescued before then...