Some Employee missing of the Reports on certain date

Summary:

I want to explain the issue we encountered. On December 10, the HR team uploaded a change affecting all employees in a specific department, effective December 11. As a result, employees from that department were missing from reports on December 10 and 11. However, they reappeared in the reports on December 12.

From my investigation, I suspect the issue is related to how effective dates are handled in the queries used for these reports. Specifically, the queries include lines like:

AND LAV.LEARNER_ID = PPSL.PERSON_ID

AND PPSL.PERSON_ID = PAAM.PERSON_ID

AND PAAM.PERSON_ID = LAV.LEARNER_ID

AND SYSDATE BETWEEN PPSL.EFFECTIVE_START_DATE AND PPSL.EFFECTIVE_END_DATE