Jabez Wilson mentions buying seven sheets of "Foolscap Paper." Foolscap Paper was named for the watermark (a court jester with cap and bells). Historically, there were two prevalent foolscap folio paper sizes: British foolscap and imperial foolscap. The British foolscap measured approximately 8.0 by 13.0 inches (203 mm by 330 mm) and was widely used in the United Kingdom for official documents and administrative records. On the other hand, the imperial foolscap was slightly larger, measuring around 8.5 by 13.5 inches (216 mm by 343 mm). This larger format was preferred in some regions of the British Empire for similar purposes. Both paper sizes represented an era when handwritten records and official documentation were prevalent, but they have since faded into history, replaced by contemporary paper standards.
At the end, Holmes slightly misquotes Gustave Flaubert (the author of Madame Bovary). The actual quotation is "L'homme n'est rien, l'oeuvre - tout", but Holmes' version essentially means the same thing. It translates as "The individual is nothing, the work is everything." Arthur Conan Doyle misquoted this in "The Red-Headed League" as "L'homme c'est rien -- l'oeuvre c'est tout.
This was the only time John Labanowski played Athelney Jones in this series, although he played a different police inspector in a later episode, "The Dying Detective". A different actor, Emrys James, played Jones in the subsequent dramatization of "The Sign Of Four".
The etching behind Holmes in his living room, is of the Reichenbach Falls, which feature heavily in Doyle's story, The Final Problem.
This is the first role Tim McInnerny played in a Sherlock Holmes story. He played Sir Eustace Carmichael in the period episode of "Sherlock" entitled "The Abominable Bride." (2016) He also played a police official of the Inspector Lestrade type in "Houdini and Doyle," a 2016 series about mysteries solved by the titular magician and the creator of Sherlock Holmes.