What are the criteria used on dictionaries to decide word classes?
Before 2004, there's no word classes labels in Chinese dictionary. In 2004, 《现代汉语规范词典》add in this label, and in 2005,《现代汉语词典》add in this label.
But it really confused Chinese people because the conception of word classes comes from English, Chinese language do not have a strict gamma system from the start. You can refer to this Zhihu post for more detailed information: Zhihu Post (In Chinese)