Although I have met Dr. Hwang of Colombus several times, his Yang's taiji has never come up. However, I did hear from others that he knew Liu's material but what you refer to as the old Yang's taiji was Yang Chien Hou's middle frame and that is what I have heard he teaches. Keep in mind that I haven't heard this directly from him but someone who studied with him before.
"Its better to build bridges rather than dig holes but occasionally you have to dig a few holes to build the foundation of a strong bridge."
"Traditional Northern Chinese Martial Arts are all Sons of the Same Mother," Liu Yun Qiao