In a grand army, you can include up to 6 duplicate Special choices and 4 duplicate Rare choices.

If choosing an army of 3,000 points or more, we consider this to be a 'grand' army, with enough patronage, cash or muscle to get a larger supply of scarce units: up to 6 duplicate Special choices, and up to 4 duplicate Rare choices.

For example, if the Empire army we discussed earlier was increased in size from 2,000 points to 3,000 points, it could then include as many as 6 regiments of Greatswords in addition to its other Special choices