Herriot's real name was James Alfred Wight; the Royal College of Veterinary Surgeons' rules ban advertising, so he took his pseudonym from the Birmingham City football club goalkeeper in the 1952 Cup Final.
Tricki Woo invites Mr Herriot to a garden party to be held on 5 August, but the film is set in 1937 which would make that a Thursday, a most unlikely day for a garden party.
Early on (and whilst James is working at the surgery) Siegfried is seen reading the "Daily Express" newspaper dated Saturday June 5th 1937. But James tells Helen in a later scene that he's only been at the practice since July.
When James and Helen are eating ice cream in Whitby, ice cream is clearly visible on James's top lip. After he has turned round all traces of ice cream have vanished.