When Password History is first enabled, ACF2 already knows what the previous passwords were. How is this possible?
When you enable ACF2 password history (PSWDHIST), ACF2 already remembers 4 passwords. How is this possible?
ACF2 maintains the current password and the 3 previous passwords in the logonid record.
Whenever a password is changed, the older passwords are bumped down in the list of previous records. This always happens, even when you are not checking or validating any prior passwords. So, when you first enable password history, ACF2 already knows any previous passwords (up to 3 previous passwords plus the current password).