When Father Eager hands the racing paper to Father Brown, he is holding it so that the large picture of the horse and the heading LITTLE is uppermost - facing Father Brown; however in the reverse angle shot this page is facing away from him.
When Lady Felicia pins the second note to the board, with its number starting with 28, the first note has it's number starting with 26. After they have investigated the date, 28th Nov, 1926, the board shows both notes have numbers starting 28.