Greetings!
From what I know, the WC was romanized as Ving Tsun in Hong Kong by Yip Man because people joked that it was bathroom kung fu (W.C.) if spelled Wing Chun... which is actually funny.
maybe a myth, yet it makes sense.
MAny people use the romanization Wing Chun, since that way it was brought here by many, thus it is hard to trademark, and many people would've been sued.
WT is trademaked, and is Leung Ting's training system. It is structured to be taught in many schools uniformly. Yet it really tastes like Wing Chun!
Also, the name Wing Chun was identified with William Cheung, yet what he does and what I've been taught, and many that do Wing Chun, is very different.
Many times the difference is in the Sifu that teaches the art, the fellow students that you train with, and your personal effort and thought you put into your training. In the end, that is all that matters.
Sincerely,
Juan M. Mercado