In Emacs one has org-mode, in Vim, vimwiki, even for plain Notepad, one can easily create a time log by pressing the F5 key. It will fill in the time and date automatically. Create a text file like day_log.txt, open it at the start of your day and press F5 key to fill the date and time. Just add couple of words on what you want to note. Done.
As for the hardware issue, his notebook was kept because he was an important person. Average Joe's notebook had a much greater chance to go into the landfill.
That's the same for today persons' digital files: Average Joe laptop goes to landfill but I'm sure presidents and whatever's files are archived by State or their families, same as they did for the paper notebook back then.