After World War II, the document was kept hidden by Japan for many years. It wasn't until 2019 that its existence became known to the world, according to the Guangdong archives.

Under pressure from various parties, Japan finally disclosed the document in May this year, allowing for a review of the document on-site, according to the Guangdong archives.

The Japanese army's Unit 8604, then officially known as the epidemic prevention and water supply department in South China, was established in Guangzhou in the late 1930s, according to Tan Yuanheng, a retired professor from South China University of Technology.