Agatha Christie's The Mysterious Mr Quin, first published in April 1930, included 11 short stories that had appeared in various British and American magazines between March 1924 and October 1929. However, it omitted one previously published story featuring Mr Quin: "At the Crossroads." This story had made its appearance in October 1926 in Flynn's Weekly, an American periodical. In December of the same year, the story was the first of six that appeared in successive issues of the British magazine The Story-Teller. The series had the overall title "The Magic of Mr Quin." This was the only Mr Quin story that had already appeared in magazine form to be left out of The Mysterious Mr Quin. In its place, a previously unpublished story, "The Bird with the Broken Wing," was added to make up a round dozen.
"At the Crossroads"/"The Magic of Mr Quin 1" did not appear in book form until 1950, as part of the US collection Three Blind Mice and Other Stories. It was given a new title, "The Love Detectives." Under this new title, it formed part of the 1991 UK collection Problem at Pollensa Bay. Christie died in 1976, which means that the story was never reprinted in the UK in Christie's lifetime. "The Love Detectives" is one of two Mr Quin stories that are not in the 1930 collection. The other, "The Harlequin Tea Set," was written for Winter's Crimes 3, a 1971 anthology edited by George Harding. The cover of that volume says "All these stories are new," which indicates that "The Harlequin Tea Set" had not yet been written when The Mysterious Mr Quin was first published. This makes it a different case altogether from "The Love Detectives."
What is the reason for the omission of "At the Crossroads" / "The Magic of Mr Quin 1" / "The Love Detectives" from The Mysterious Mr Quin? Why was the story left uncollected for 20 years in the US, and more than sixty in the UK?