Ditko was never offered the artwork from Amazing Fantasy #15. The spokeswoman for the LOC said she was told by the donor that he (notice it seems the donor was a man) had contacted Ditko to see if Ditko had any objection to the donation. The donor told the LOC that Ditko said, "I don't care what you do with it." The LOC spokeswoman also reported the donor had told her he had other important silver age Marvel art which he might be willing to donate. The donor asking for anonymity, and declining an estimate of value for the art meant he would not be able to claim the value of the artwork as an income tax deduction.
To date Ditko has released no comment on the donation. I've always thought it was incredible that the LOC didn't insist on speaking to Ditko rather than accept the word of the donor.