Curaçao Orange Parent Stock
The simple fact is that the formal name of the Curaçao orange, Citrus x. aurantium var. curacaviensis, means that it is a variety of the Seville orange (Citrus x. aurantium).
There is a Wikipedia entry that asserts that the parent stock of the Curaçao orange brought to the island by Spaniards in 1527 was the Valencia orange.
That page cites a book, Jews of the Dutch Caribbean, by Albert Fredric Benjamin.
But, Benjamin states on page 49 of his book that the Spaniards brough "a bitter orange" to the island in 1527.
That could not have been the sweet Valencia orange.
It would have been the Seville orange.
Furthermore, Benjamin cites the book, "Historical Dictionary of the French and Netherlands Antilles", by Albert Gastmann.
Gastmann states in his book that it was the Seville orange.
There is another very simple proof that the Valencia orange could not have been the 1527 parent stock of the Curaçao orange: the Valencia orange was first hybridized in California in the 1860's.