During Lavinia's funeral, Thomas is seen wearing his footman's livery, complete with white tie, underneath his overcoat. Like the rest of the men present, Thomas would have been wearing his usual church-going suit, complete with a black cravat as befits a funeral. There's no way he'd appear at a funeral wearing white tie.
The goof item below may give away important plot points.
When Mr Bates is arrested by police officers the handcuffs used are a ratchet type, which were not in use by British police until the 1950s. The correct type should have been a Hiatt Darby or a Dowler Darby non-adjustable single locking key lock model.