Matthew's quotation, "I am the Cat that walks by himself and all places are alike to me," is from Rudyard Kipling's short story "The Cat that Walked by Himself" published in his 1902 pourquoi, or origin story, collection, Just So Stories.
While pushing Matthew, Mary says she'll develop arms like Jack Johnson. Johnson was the boxing heavyweight champion of the world from 1908 to 1915 and the first African American to hold this title.
When Patrick Gordon tells Lady Edith about his time in Canada after the Titanic sank, he mentions having been part of "Princess Pat's regiment". The regiment he's referring to is the Princess Patricia's Canadian Light Infantry. It was named in honour of Princess Patricia of Connaught, a granddaughter of Queen Victoria and a very popular public figure in Canada.
"Patrick" mentions that he was rescued by Fifth Officer Lowe, the only one who came back. Only four men were picked up that night, one of which died. Patrick's story could have easily been checked. It's true that Fifth Officer Harold Lowe came back but it wasn't right away because Lowe was afraid of the boat being swamped by survivors.