Ouyang Feng was very familiar with XL18Z and Hong Qi was very familiar with Hama Gong. It's why each was trying to come up with new styles to fight one another (begs the question why Hong Qi never just used the full Dog Beating Stick). When they fought each other on Peach Blossom island, they were coming up with new moves on the fly to no avail. Ultimately, Ouyang Feng launched an internal power attack. Just because you know another's art doesn't automatically give you an advantage especially if they know your art as well. I think Lin Chaoying would be able to identify similarities between Guo's 9 Yin and Quanzhen arts just as Hong Qi was able to identify that Guo had Quanzhen internal.