Well... If there's no RTC in the machine I must admit to being wrong there isn't any solution to date a file without convenient hardware. Odd choice for the default date though.
True there are plenty of buggy open source projects around developed for free on peoples spare time. In many cases free but not fantastic. All the same I'd say that projects like Sigrok and the AVR transistor checker are open-source successes.
On the other hand there are also plenty of buggy closed-source products sold, in which case you're not really getting what you pay for iMHO.
1979/12/31 is somehow special day in computers.
it is computers worlds last day.... before...
... MS-DOS time start 1.1.1980. (but Mr MSDOS was poor boy and die to this happen computer words perhaps most bad mistake... there was at this time available also others, lot of more advanced at this time but Mr BG did not have money for these. But all we know, best do not always win... more popular may win.)
UNIX time (as also inherited to child of UNIX aka Linux) have start 1. January 1970 00:00 UTC (its value is zero, from this point UNIX time tics up. Just now when I am writeing this (not message time stamp what is later), current Unix epoch time is 1624545423
btw, some of us remember one old trick with Siglent spectrum analyzer and fooling its system time...