The sys_history_set and sys_history_line tables are 'populated' as needed by ServiceNow based on the data in the sys_audit table.
The sys_history_set, sys_history_line, and sys_audit tables serve as integral parts of the internal ServiceNow code. The code in the GlideHistorySet API is used exclusively by ServiceNow in various out-of-box scripts, however, the methods in the API are not intended for customer use. If a customer attempts to implement a method in the GlideHistorySet API, or to change the values or suppress the update of a record in those tables, then an unexpected result or an error may occur.
Customer support does not support the customer's use of the GlideHistorySet API, or any modification to the normal operations or values in the ServiceNow tables sys_history_set, sys_history_line, or sys_audit tables.