You create a file on 30.09.2010, back it up and lose it due to hardware failure on 12.07.2022. When you restore the file from your backup to your device it will most likely be stamped as created 12.07.2022 even though originally it was created before that. If you name your file manual_2010-09-30.pdf you always know the date it was created and sort it by that filename.