Continuity mistake: Towards the end while Brian and Welch are talking at the hotel, the sun on the wall changes between shots.
Continuity mistake: When Billy and his daughter are at Moreen's grave the sun changes between shots.
Factual error: Michael's wife meets with Longo in prison, and she has an iPhone. The trial was in 2003, 4 years before the introduction of the iPhone in 2007.
Factual error: There are several scenes in a field of barley. Tramlines are seen. Tramlines in crops were invented in 1975 to allow tractors and sprayers to drive up and down fields. Sunset Song is set around 1914, 61 years before tramlines were invented.