Analysis of information sources in references of the Wikipedia article "T-X program" in English language version.
The T-50A designation has been set aside for the Lockheed Martin/KAI Golden Eagle advanced jet trainer, which is marketed under the company designation T-50. The U.S. military has currently no plans to procure this aircraft. Obviously, the official T-50A MDS designator was reserved for the Golden Eagle so that it wouldn't be inadvertently assigned to another aircraft model (leading to confusion between two different "T-50" trainers).