All There in the Manual: Sister Bernadette's first name is revealed in 2x08, but her pre-convent surname of "Mannion" was only revealed in the credits list.
Anachronism Stew: Largely averted, but there's a particularly glaring example with the Establishing Shot of The London Hospital, which shows the name "The Royal London Hospital"—an appellation it didn't get until the Queen's visit in 1980.
Approval of God: Long before the memoirs were filmed, Jennifer Worth spotted Miranda Hart and knew she'd be perfect for the role of Chummy Browne. Hart agreed to play Chummy if the books were ever filmed. The rest is history.
Artifact Title: In this case, Artifact Portmanteau Couple Name. The Turners hadn't yet had their first names (or in then-Sister Bernadette's case, her pre-Order name) revealed onscreen while the two were falling in love in series 2, so the fandom christened them Turnadette (Turner and Bernadette). The final episode of that series revealed 'Shelagh' and 'Patrick', but the portmanteau has remained 'Turnadette', even though the former has now spent longer onscreen as Shelagh Turner than she did as Sister Bernadette.
The Cast Showoff: Possibly the most understated use of this trope in the history of television. Sister Bernadette leads the hymns for prayer, and that's Laura Main, a trained soprano, actually singing. All the vocal solos are hers.
Stephen McGann, who plays Dr Turner, has been fondly nicknamed by his fanbase "the Human Disaster" (for his questionable sartorial choices and general adorkableness). This nickname is as official as it gets; to the consternation of the whole fandom, it appeared in the Radio Times.
Similarly to the above, Laura Main has been nicknamed "the Pocket Soprano" because she is tiny and a soprano.
"DTE", or "Dr Turner Effect", refers to Stephen McGann — and his character, Dr Turner — making women everywhere swoon. Any photograph in which he looks particularly attractive will be labeled with "DTE".
Show Runner Heidi Thomas is often referred to affectionately as "The Queen" in the fandom on Tumblr.
Sharon Small (Nora Harding, episode 2x05) previously played DS Barbara Havers on The Inspector Lynley Mysteries. Jenny Agutter (Sister Julienne) made a guest appearance in episode 3x03 of that programme, A Cry for Justice, playing Jemma Sanderson.
Real-Life Relative: Screenwriter/show creator Heidi Thomas is married to Stephen McGann, who plays Dr Turner. (McGann good-naturedly grumped that just because he's married to the head honcho doesn't mean he gets a preview of what's coming; he had to wait to find out whether Sister Bernadette and his character were going to end up together until he got his script. For the record, they did.)
Episode 3x01 dealt with cystic fibrosis because Jenny Agutter lost two infant siblings to the disease, and her niece has it as well; she has since focused most of her charity work on finding a cure.
Sister Monica Joan's struggles with dementia are very much coloured by the fact that Judy Parfitt's real-life husband died of Alzheimer's, which obviously shapes her performance.
In series 4, Doctor Turner touts an anti-nausea medication for pregnant mothers.
Dr Turner: "The tablets are known as Distaval. The magic ingredient is called thalidomide.'
Shipper on Deck: Stephen McGann and Laura Main ship their characters almost as desperately as the fans do. Possibly more. Doubles as Approval of God as Laura Main said that she's proud of the Turnadette shippers and glad the pairing is so popular.
Star-Making Role: For Jessica Raine, Helen George, Bryony Hannah, and Laura Main.
Throw It In: "The Road Scene" was originally planned to be shot in bright sunshine, but on the day of filming, the crew encountered a classically English misty fog. Cast and crew alike raved about the effect, with Stephen McGann citing the symbolism of "Laura [Main] coming out of the fog" in particular as lending the scene a mystical, dreamlike quality that fit the romance perfectly.