Because Jiaqing was the next emperor, his name was different from others.
The first reason is that Emperor Qianlong was a jade fanatic
Emperor Qianlong can be said to be one of the wise emperors through the ages. His biggest hobby is collecting jade, so each of his sons will have jade. Next to the word, not only is his son named like this, but 800 of his poems handed down are about jade, which is enough to prove how much he likes jade.
The second reason is that Jiaqing is the next successor
But he has a son whose name does not contain Yong. Why is that? It's very simple. That's because Jiaqing is the next successor, that is, the throne is his. If there are no accidents, you must know that in ancient times, people were very careful not to conflict with the emperor's name. It was a great disrespect to the king, so Qianlong would have to advance in advance. Help him change his name, so as to avoid trouble in the future. A lot of people have to change their names. For example, before Kangxi became emperor, his name was Xuan Ye. Then during his reign, no one was allowed to use these two words.
Even the Xuanwu Sect had to change its name. Because it conflicted with the emperor's name and was very bad for the emperor, the ancients changed its name to Shenwu Sect.
The third reason is that Jiaqing changed his name
But when it came to Yongzheng, it still had to be changed, because when Yongzheng came to power, his name was Yinzhen, and his brothers all had Yinzhen. So what to do? Yongzheng changed his name to Yun, but how could Jiaqing change it? The word Yong was so common that no matter how I changed it, I simply changed Jiaqing's name to Yong Yan, so that no one could compete with him. Everyone was happy.
To summarize, as long as there is a prince in the Qing Dynasty whose name is different from the other brothers and sisters, it can basically be confirmed that he will be the next emperor. Their rules are very rigid, so they are very regular.