(spoliers) Why did bad guy bring the REAL manuscript for sale at end?

*****SPOILERS THROUGHOUT********



In my post here, I try to explain the nuts and bolts of the who-done-it -- what motivated the bad guy's actions and how Sloane (Robt Montgomery) solved the case. I enjoyed the movie a lot, mostly for the Thin Man-style characters. The plot confused me and most others. I re-played the movie a number of times to finally understand the plot, but, frankly, have come up empty. Perhaps some of you can answer some of my queries: the main one being why on earth, at the end of the movie, did Charlton bring down the REAL manuscript to sell (for the Torrents) to Oates?

HERE IS WHAT I UNDERSTAND:
(1) Torrent (an honest and rich rare book collector) owned the genuine manuscript, which was worth a half-million dollars, a fortune at that time.

(2) Charlton (Torrent's stock broker and friend) and Wilkes (a master forger and Torrent's librarian) stole the genuine manuscript, replaced it with a forgery and (secretly somehow) sold the real (genuine) manuscript to respectable book collector Stockton.

(3) A year later, the plot starts to unravel. Torrent needs money and is about to sell his (unknown to him) fake manuscript. Somehow he learns (off screen) that Charlton had stolen Torrent's real manuscript. So Charlton (a) kills Wilkes, his accomplice, to silence him, and (b) kills Torrent (to silence him too) and at the same time steals Torrent's fake manuscript.

(4) Meanwhile Slone, who is secretly investigating suspected shenanigans at the Torrent library and staying at the Torrent mansion, knew that Torrent's manuscript was a fake, but didn't let on that it is a fake. That was very clever of Sloane -- it proved fruitful in turning up Stockton, who had the real manuscript.

(5) News of the murder of Torrent and the theft of the purported real (but actually fake) manuscript reaches Stockton, who becomes worried that maybe his (real) manuscript is a fake. Stockton phones the police; he tells them (and Sloan) that he has another copy of the manuscript. He doesn't bother to tell them how he acquired it, but he travels with his (real) manuscript to visit book expert Sloane and the police. Charlton somehow learns of this, and kills Stockton and steals the (real) manuscript before Stockton can meet Sloane and the police.

(6) Now we come to one of the most important and puzzling things in the movie.
Chartlon, who has killed Stockton and taken Stockton's (real) manuscript, now has both manuscripts -- the fake one from Torrent and the real one from Stockton. He (a) hides the fake one in the bedroom of the son of Torrent so as to incriminate the son and allay suspicion from himself (This ploy is successful, by the way; the police discover the fake manuscript hidden in the son's room.); and (b) a few days or so later, he (acting as broker and family friend of the Torrents) takes the REAL one to Sloane's office to sell it to Sloane's client, Mr. Oates. (Why did Charlton take the real one to Sloane's office?)

(7) At the end, Charlton is caught in Sloane's trap. Sloane knew with his own eyes during his visit that the manuscript Torrent had in his library was a fake. He never let on publicly that it was a fake. Charlton, thus, believed that the fake was still undetected. When Charlton went to Sloane's office to sell the manuscript, Charlton brought down the REAL manuscript . Why???? Only the murderer of Stockton could have the real manuscript! (Charlton said, at Sloane's office when ID'd as the murderer: "So you did detect the forgery! I wish I had known that!")


WHY DID STOCKTON BRING THE REAL MANUSCRIPT TO SLOANE'S OFFICE?
Maybe someone smarter than I can explain why Charlton took the REAL manuscript down to the expected sale at Sloane's office. For one thing, it was the manuscript Stockton had, so only the murderer would have it to bring down. It had to be somewhat different than the fake one, so Sloane might have noticed the difference in his office. (All along Sloane had seen only the fake. He had never seen the real (Stockton's) one.)


I can see why Charlton hid the FAKE manuscript in the son's room. I think the best explanation is that Charlton did what most villains do -- they put icing on the cake by making a too-complicated scheme to implicate someone else. Usually this is unnecessary and is too complex, and thus leaves clues to their guilt. Here, Charlton wanted to hide the manuscript in the son's room, but after Stockton was killed (at the Torrent mansion) there would be too much excitement and witnesses running around for Charlton to go to the son's room with the REAL (Stockton's) manuscript. It would be safer and easier for Charlton to hide the fake manuscript (that he possessed for some time, since Torrent's murder) in the son's room prior to the Stockton murder. (Maybe Charlton had hid the fake manuscript there right after the Torrent murder!) ... ..... ....... Also perhaps Charlton was super greedy and planned to sell the real manuscript long after the dust settled, if the Torrent family didn't permit him to sell the manuscript to Oates. (I had thought once that perhaps Charlton was planning to flee with the proceeds of the manuscript sale to Oates.)


It seems to me that Charlton had nothing to gain and everything to lose by selling the REAL (Stockton) manuscript to Oates through Sloane. For if the fake one is spotted in Sloane's office, so what -- it's the same one Torrent had for a year, the one taken from him, put in the son's room and then in police or Torrent family custody and finally given to Charlton to sell to Oates. But if a different one (different than the one Torrent had for the last year) is spotted in Sloane's office, it is "curtains" for Charlton -- only the murderer of Stockton could possess it! Sloane had already passed (approved) on the fake one. If Charlton brought down the fake one (the one found in the son's room), Charlton still had the real one, which he could sell on the black market later on, if he wished.

There is one explanation for Charlton's actions, but it doesn't fully satisfy me. Charlton could have thought that selling the REAL one to Oates would end the matter: no book expert then or in the future could doubt the genuineness of the manuscript, and there would be no fake manuscript to compare it to. Maybe Charlton thought he was being super conservative in bringing down the real one: in case another expert would be with Oates for the sale, that expert might detect the forged copy. BUT selling either the fake or the real one (for the Torrent family) to Oates in no way would avoid a police investigation, for there still was the matter of the Stockton murder and how Stockton acquired his copy of the manuscript. And if the fake one was sold to Oates and later turned up to be certified as fake, so what? -- there was always dead criminal Wilkes to blame for that.