She doesn't. "Mr. X" was conceived by fans due to Japanese material explaining T-00 is a "T-103 Tyrant" not being translated in the West. ToyBiz picked up on a fan name and made it the name of their toy, and that was copied by WildStorm for their copies and Perry for her novels. If you look closer, you'll notice that "Tyrant" was assumed to be the name of the T-002 only.

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