Due to an overloaded long weekend, I am a bit behind on this, of course.
Up to 813, one notices a progression in LeBlanc's depiction of Arsene Lupin. Lupin gets inreasingly dark, ruthless, and disturbing. He is not merely a brilliant thief; he is a dangerous man. This contrasts with the earliest views we get of him, which is of someone who is more of a trickster, the kind of person who (temporarily) outsmarts a version of Sherlock Holmes by finding a way to lock him in a house overnight at a key point, but thoughtfully supplies a picnic dinner out of both a respect and a desire to tweak his opponent's nose. He begins charming and stylish, in very careful control of his own public relations; he stays stylish, but in The Hollow Needle and 813, he loses control of his public relations, and he becomes much less charming. Some of this is just that the stories become a bit darker and Lupin's difficulties become deeper -- in Arsene Lupin vs Herlock Sholmes, he is playing a game with a clever opponent, but in The Hollow Needle, Lupin has too many clever opponents and cannot outmaneuver them all simultaneously, resulting in tragedy, and in 813, Lupin is in a life-and-death struggle, with all of Europe on the line. He's still very competent, but he doesn't really seem quite the miraculously hypercompetent character of the earlier stories; we find him often anxious or afraid or angry. This varies a lot, but it is certain that he becomes, overall, a darker figure.
813 was originally intended to bring an end to Lupin, but in returning to him, LeBlanc faced a question of how to return to him. His solution to the problem was not to continue the story onward but to go back in time, and this provided the opportunity to return to the charming and humorously mischievous Lupin of the earlier stories. We saw this to a limited extent with The Crystal Stopper, but we find it even more in the short stories and novellas written around the same time. These were collected in Les Confidences d'Arsène Lupin, which is usually translated into English as The Confessions of Arsene Lupin. All are set before The Hollow Needle. Most of them were originally published in journals in 1911, before The Crystal Stopper came out, but three were published in 1912 or 1913. When the English translation came out, it also included a short story from 1927. This makes for ten stories:
1. "Two Hundred Thousand Francs Reward!..."
2. "The Wedding-Ring"
3. "The Sign of the Shadow"
4. "The Infernal Trap"
5. "The Red Silk Scarf"
6. "Shadowed by Death"
7. "A Tragedy in the Forest of Morgues"
8. "Lupin's Marriage"
9. "The Invisible Prisoner"
10. "Edith Swan-Neck"
So this will be the next fortnightly book.
