When Inge visits Philip, he pours the same glass of milk twice.
Footballer Doyce collapses on the football field and is pronounced dead, his girlfriend dashes to his flat to retrieve some letters and as she's leaving the hall porter is seen to be looking at a paper with the headline about Doyce's death which is some what too early.
The final goal in the replayed match is awarded, despite the ball obviously not crossing the goal-line.
When Slade and Clinton are searching Doyce's flat, at one point Slade leans on the telephone wire and accidentally pulls the receiver off the hook.
The Gunners/Trojans replay kicks off at 3pm on Wednesday 26th April (dating the film to 1939), with the original match therefore presumably being held on Saturday 22nd April - which is the date of the "Evening Globe" newspaper seen detailing the police's search for a blonde woman in relation to the death.
There seems to be no reason for the murderer to incriminate him/herself at the end, as the clue contains no evidence.