Interesting article in smithsonian a couple of years ago asking well known astronauts and other military greats how they kept track of their flight time.i was amazed at how many , after the first few years, never even made entry's any further! When I was young there were many who started training at a local airport and then quit after a time for any number of reasons, leaving their log books at the airport. One could , if they lost theirs , find one with approximate hours of instruction and commandeer it. There was a big pile of them amassed over many years. Personally , I often flew and never marked it in my log, like if I flew after work for an hour or so , etc. seemed silly. If I'd flown for a career I would have been far different.