The date and time both has been changed. The reason you don't see it displayed on the LCD is because the "clock.pc5" program loaded in the PLC when it was shipped from factory only displays the date once upon power on reset. It does not keep displaying the date so the LCD doesn't show the new date.
What you need to do is to do an on-line monitoring and click on the "View" button and you will be able to see the new date in the Real Time Clock. You can then click on the "Reset" button and this time the LCD will show the new date.