Part of the reason for the Investiture Calamity was that the Heavenly Court had too many vacancies among its officials and needed to conscript labor.
If even the Heavenly Court was short of labor, the Netherworld went without saying.
Only during the Investiture of the Gods was Huang Feihu appointed Great Emperor Dongyue, put in charge of the Netherworld's eighteen levels of hell. All matters of life, death, and transformation involving humans, gods, immortals, and ghosts had to be examined and approved by Dongyue before they could proceed.
Only then did the Netherworld gain a complete set of rules and regulations, along with someone at the very top.
"All matters of life, death, and transformation involving humans, gods, immortals, and ghosts had to be examined and approved by Dongyue before they could proceed." This meant that after humans, beasts, immortals, demons, spirits, and monsters died, whether they became humans, gods, immortals, or beasts required Great Emperor Dongyue's approval.
This was also called reincarnation.
In other words, before the Investiture of the Gods, the Netherworld was a mess.
Reincarnating was possible, but no one supervised it, so souls just fucking reincarnated at random.
For example, the parents of Xuandu, who went by the alias Wang Chan, the Ghost Valley Master, were accidental products of that fucking random reincarnation. The two had already been entangled in their previous lives, but one was reborn from a dragon maiden into a human body, while the other accidentally became an ear of rice. This led to a tragedy, and even caused Xuandu to pin the blame on the Heavenly Emperor.
True, mighty beings could interfere with reincarnation-Nezha was the result of Yuanshi Tianzun doing just that. But the Heavenly Emperor oversaw the Three Realms and was busy eating Flat Peaches and drinking Immortal Dew. Clearly,