Dumbledore did not doubt the truth of Manus's information. Manus had not even known beforehand that he wanted to find the Resurrection Stone, so there was no reason for him to invent a lie specifically to deceive him.
As for why Manus knew that the Resurrection Stone was in the Gaunt family's possession... that was probably knowledge passed down through the King Family. Perhaps their ancestors had intermarried or something. Such things were not entirely impossible.
Considering that Manus even knew the Resurrection Stone's effects were modeled on the creation of ghosts, and that the results were inferior to actual ghosts...
The generation in which the King Family and the Gaunt family had intermarried seemed to have been quite close. Even the secrets of such a treasure had been shared with the other family, which had gone so far as to record them.
The Gaunt family's own descendants probably no longer knew about any of this, did they?
Recalling the mental state of the Gaunt family members he knew of, Dumbledore shook his head. He decided that the marriage between the King Family and the Gaunt family must have taken place a very long time ago.
At least the Gaunt family members back then probably had not been quite so mad.
With their main business concluded, Manus did not stay much longer. After discussing magical research with Dumbledore and having him sign the parchment for joining the Wizard Sage Party, Manus took his leave.
Dumbledore wore a peculiar expression as Manus left. He had never imagined that, at nearly a hundred years old, he could still be taught a lesson by a student when it came to signing a magical contract...
Who on earth taught you to hide clauses in decorative patterns?
"Was it a little wrong of me to