First, for flights not involving USA, they do it by the weight concept, not piecewise. You can check as many pieces of luggage as you could reasonably want to, as long as the weight limit is adhered to.

Do you have any *A status? Silver gives you an extra 10kg; gold, 20kg.

However, TG has been known not to be too strict about their weight limits. Of course, that's never a sure thing.