There should be, although how much might be debatable. Ultimately - I think the "sweet spot" is the version you didn't include:

CREATE NONCLUSTERED INDEX IX_OrderDetailDateProdSold ON dbo.OrderDetail

( OrderDate ASC, ProductID ASC) INCLUDE (QtySold);

The short version as I understand it to make the "ideal" covering would be:

- columns appearing in the WHERE, FROM, GROUP BY and ORDER BY should appear in the "main part" of the index.

- columns not otherwise included that appear in the SELECT or HAVING go in the UNCLUDE clause.

Technically - since the "main part" is what the B-tree is based on - by keeping the main part as skinny as you can, you get better perf, while avoiding the bookmark lookup with the INCLUDE stuff.