There are probably two reasons. First, the teaching materials in different regions are different and will change. Second, many people are not curious. These reasons have led to no one asking this question for such a long time.

First, junior high school students point out that it is wrong to use coins in history textbooks. In the summer vacation of 2020, junior high school student Gu Zexing browsed the compulsory education textbook Atlas of Chinese History. When he read the book, he found a problem. Historical Atlas is a book to help students supplement historical objects or events and people. There are two photos of ancient coins in one page of this historical atlas. During the reign of Emperor Xiaowen in North Africa, it was marked as Taihe Wuzhu, Xuanhe and Bao Tong. Gu Zehang knew that Xuanhe was not the title of Emperor Xiaowen, but the title of Song Huizong.

So he checked a lot of relevant information and confirmed that Xuanhe Bao Tong should be the currency of Song Huizong period. In order to prove it, he found a famous scholar to prove it, and the scholar told him that it was really wrong. Later, the editor of this atlas also directed this matter, saying that this graphic will be revised in the future.

Second, the teaching materials in different regions are different and will change. First of all, the textbooks are different all over the country. For example, all the books I use there are from Shandong Education Publishing House, and some places use People's Education Edition or other editions. Due to different versions, some versions will have problems and some versions will not. Moreover, textbooks will be changed, not always used, and textbooks will be changed in a few years. So it's not that no one has discovered it for many years, but no one has really put forward this matter for several years.

Third, many people are not curious about knowledge, which is actually the main reason. This history album is an auxiliary book. I seldom use this book here, and there are few students, so the probability of finding this problem is even lower. Moreover, even if someone reads the historical atlas, they may not be particularly careful when reading the book, and they may think it is wrong and will not research it. Others, even if they found out, wouldn't mention it if there was something wrong with this place. After all, it's too much trouble to repeatedly verify. Combining these aspects, it is the reason why this problem has not been discovered.