Try setting the clock on the remote press [FUNCTIONS] go to SETUP menu - locate the CLOCK option (it should be under 'OTHERS' in the setup) and set the current time, press [ENTER/OK] to store if necessary, then press [RETURN] to exit the setup. Once clock is set correctly, future DVD thumbnails will show the actual date/time of recording in this (and similar) model combo units. If auto clock setting is not possible, set it manually as above.
I assume in spite of the wrong date/time, your DVD recordings have been successful. Incorrect clock and date setting usually only affects timer recording for VHS.
If you have lost or misplaced your original owner's manual, you can download a free pdf version (for Region 1 model) from:http://www2.panasonic.com/consumer-electronics/support/Video/DVD-Recorders-Players/DVD-Recorders/model.DMR-EZ48VK
or, if you live outside USA, download the 'Australia/NZ' pdf version of the manual (for Region 4 model) from:http://www.panasonic.com.au/Products/DVD+and+Blu-ray/DVD+-+Players+and+Recorders/DMR-EZ48V/Downloads
either one of these will provide you a full copy of the original user guide/setup including clock.
All free. Hope these suggestions help.