CREATE TABLE table_69221 ("Name" TEXT, "Father" TEXT, "Birth" TEXT, "Marriage" TEXT, "Became Countess" TEXT, "Ceased to be Countess" TEXT, "Death" TEXT, "Spouse" TEXT)

When was the marriage of the person who died on 17 December 1471?
SELECT "Marriage" FROM table_69221 WHERE "Death" = '17 december 1471'
SELECT "Marriage" FROM "table_69221" WHERE "Death" = '17 december 1471'