Chapter 19, p. 897-898. Here, it's revealed how Zhang Wuji was able to completely master the Divine Powers of the Nine Suns. When he was tied up in the Baggy Monk's magical bag, he tried using his power of the Nine Suns to break out of it. While he was doing this, the magical bag became a pot, and the power of the Nine Suns was building up, almost like steam. Inside this cloth "sauna", Zhang Wuji's power of the Nine Suns grew more and more potent. Like steam to raw flower to make a bun, all of the pressure points on his body were "opened," so that he was able to master the powers of the Nine Suns even sooner, and with greater potency. The result is that Zhang Wuji is now the most powerful of all the heroes of wulin.
p. 901-02. In the book, Xiao Zhao (brightness) first appears to be a very ugly girl. This is because of a birth defect, which is feigned. In the 1994 TVB version of this story, Kong Hay-man acts this part like the novel describes. In the 1986 TVB version, Siu May-kay doesn't.
Chapter 21, 960-63. The 1994 version portrays the batthle with Zhang Wuji and Song Weixia at Bright Shining Peak fairly faithfully to the novel. Song Weixia is one of the elders of the Hong Dong school for martial arts. He had been practicing the school's highest and most powerful set of wugong called the Fists of Seven Wounds, and he slowly began to injure his own physical health. He had been feeling some pain, but because he was afraid of facing these injuries, and at the same time he didn't want to lag behind his brethren in mastering this set of fist-combat arts, he ignored the pains and continued.
When he meets Zhang Wuji at Bright Shining Peak, Zhang Wuji tries to educate Song Weixia, but Song is too proud to consider the advice of a man more than half his age. Moreover, he attacks Zhang Wuji to show off how powerful the Fists of Seven Wounds are. Zhang Wuji, however, was able to absorb the force of the fists, neutralize it and surprisingly, returns the force of the attack to Song Weixia in the form of jinqi 九陽真氣, pure energy of the Nine Suns.
Song Weixia then realizes that Zhang Wuji was sincere in his advice, so he praises and graciously thanks Zhang Wuji for returning Song's hostility with kindness.
In the 1986 version, this is scene is omitted. One reason I could think of is because the scene is not crucial to the main conflict of this battle at Bright Shining Peak. I believe it was written more to reveal the forgiving nature of Zhang Wuji.