This will be the first season of "Endeavour" in which the character of Joan Thursday makes no appearances. (This is because Sara Vickers, who plays her, had had a baby shortly before shooting began).
This episode features the first-ever conference of the Women's Liberation Movement, a real-life event which took place at Ruskin College, Oxford. One of its organizers was Sally Alexander, a prominent feminist of the early '70s. Alexander was also the first wife of actor John Thaw, the original Inspector Morse, and the mother of actress Abigail Thaw, who appears regularly in the "Endeavour" series in the role of reporter Dorothea Frazil. Alexander is portrayed in a non-speaking role by Molly-Mae Whitmey, real life daughter of Abigail Thaw and the granddaughter of John Thaw and Sally Alexander.
This story refers us back to the pilot episode of "Endeavour" when Ludo reacts excitedly to the discovery of a recording by Rosalind Calloway in Morse's record collection. "Rosalind Calloway" (aka Mrs. Stromming) was one of the central characters in that first "Endeavour" story, a singer whom Morse idolized and was thrilled to meet. The story ended with her suicide; perhaps this is why, in "Oracle", Morse off-handedly gives the recording away to Ludo, claiming he hasn't listened to it for years.
At the end of the closing credits, a dedication appears to Barrington Pheloung, composer of the "Inspector Morse" theme, as well as much other music for "Lewis" and "Endeavour". Pheloung died in August 2019.
Chief Inspector Thursday briefly refers to a TV personality, David Nixon. Nixon (1919-78) was a well-known figure on British television in the 1950s, an illusionist and comedian featured in many a BBC series, from "What's My Line?" to his own variety show, "Showtime". He often wrote his own material and also very occasionally acted.