The dinner conversation about the limits of Holmes' knowledge (literature, astronomy, politics, etc) is taken from a list made by Dr. Watson in Sir Arthur Conan Doyle's first Holmes story, 'A Study in Scarlet'.
Ian Hart reprised his role as Dr. John Watson in Sherlock Holmes and the Case of the Silk Stocking (2004). He also played Sir Arthur Conan Doyle in Finding Neverland (2004).
When Holmes and Watson are seen at Exeter railway station, behind them is a truck marked "SR". This would refer to Southern Railways, which was not formed until 1923, some time after the period the film is supposedly set.
When Stapleton points out a rare orchid he's found on the moor, we see a huge pink orchid of the kind sold in supermarkets as a table decoration. The orchids of Dartmoor are small wildflowers.