The Zheng family of the Marquis of Yong 'an was a title given to them when the great Zhou Dynasty was established. The current Marquis was also Zheng Qiu's father, and he was the fourth generation.
At that time, the title was given to the fifth generation. In other words, after Marquis Zheng's son inherited the title, if the Zheng family did not receive another title, their title would be gone.