u/harrypottered

JKR wrote a scene she tried to use in both CoS and GoF that never made it in. From her archived website:

Theodore's father (the same Nott who was badly injured in the closing chapters of 'Order of the Phoenix') goes to visit Lucius Malfoy to discuss Voldemort-related business and we see Draco and Theodore alone in the garden having a talk of their own.

Together these two Death Eaters' sons discuss Dumbledore's regime at Hogwarts and Harry Potter, with all sorts of stories that the Death Eaters tell about how this baby boy survived the Dark Lord's attack.

Later on, she wrote in her Pottermore article on Draco Malfoy which theory Lucius believed most:

Many different theories had been in circulation for years as to how Harry survived what should have been a lethal attack, and one of the most persistent was that Harry himself was a great Dark wizard … Lucius Malfoy, was one of those who subscribed most eagerly to the theory.

My guess is this scene was originally an alternate POV cold open like the ones in PS, GoF, HBP, and DH. It would've set up the red herring of Harry being the Heir of Slytherin, but also tipped the hand too early that Draco wasn't the culprit in CoS. If that was the case for CoS, I could see why JKR cut it despite liking the scene so much.

Still, it’d be cool if they added some form of that Draco and Theodore scene with a cutaway to their fathers talking inside Malfoy Manor. I’d like to see Lucius theorizing that Harry could be a Dark Wizard after hearing he’s a parselmouth (a magical trait unique to descendants of Salazar Slytherin). Nott Sr., whose father authored the Sacred 28, would be a natural source on wizarding genealogy.