The publication calendar stated that September CPI data should have been released on October 5th: http://kostat.go.kr/portal/eng/resources/1/index.static
However https://kosis.kr/statHtml/statHtml.do?orgId=101&tblId=DT_1J17001&conn_path=I2&language=en as well as press release shows that it was released on October 6th.
Could I know why there is a discrepancy?
Statistics Korea / 2021-10-12
Thank you for visiting the KOSIS website and showing interest in the dissemination of CPI data.
According to the publication schedule of CPI data, Statistics Korea was supposed to release September CPI data on October 5th. However, under the government's alternative statutory holiday program (substituting holidays for all public holidays that fall on weekends) which was revised on August 4th, 2021, October 4th became an alternative holiday. Therefore, due to the data security problem, September CPI was disseminated on October 6th, 2021.