This is the only episode to take place entirely in one time period.
This episode takes place in London, England, UK on November 19, 1889.
This was the last episode of the series.
Phineas Bogg learns that Jules Verne's character Phileas Fogg in AROUND THE WORLD IN EIGHTY DAYS was possibly named after him since Phineas says he met Jules Verne in person.
221B Baker Street was Sherlock's address in the stories, but that address never really existed. In Connan Doyle's time Baker Street did not go that far. When the street did go that far 221 would have been in the middle of a very large office complex. Years later a Sherlock Holmes society got its 229 Baker Street clubhouse formally relabled as 221B.