Once upon a time millions of coders had to sit down and fix programs that had been written by other coders who forgot about four digit year numbering.
In some companies. But not in others where internal dates were stored as number of days since Jan 1, 1901 and there was a central date routine called to convert between any two date formats. I remember in 1996-1998 that although we spent those two / three years testing everything, there was very little that needed “fixing”.
ICL's (British company) operating systems did that. Handled dates long into the future. All you had to do was put calls to the built in date routine into your programs. Didn't stop people who used their computers screwing things up, though. Yellow Pages, for example, introduced a system in the 1980s for storing all their subscriber data. Directories could be generated & printed straight from the database, with the standard lline entry or additional ads. That worked pretty well, as I recall - in 1988.
All dates on the database were stored as YYDDD.
When I (a humble contractor) suggested in a meeting at the end of the 1980s that given the lead times on major developments, future dates on the database, & the mad rush for staff there would be in the late 1990s, perhaps someone should pencil in as a point for consideration changing the date handling (just converting to CCYYDDD would do it) in a few years, the head of IT laughed out loud, & mocked me.
In 1998 I was an employee of another company, & among other things, fixing programs that foolish people had rendered incapable of functioningly correctly in 2000 despite the availability of a built-in date function that worked perfectly, e.g. a bit of code in a program to work out whether a year was a leap year or not (Doh! No need! Just use the bloody built-in routine!) which assumed that 2000 would not be a leap year. The silly billy thought that just because 1800 & 1900 weren't leap years & 2100, 2200 & 2300 wouldn't be, that 2000 wouldn't be. It's
except when it's divisible by 100, & not by 400. Tut tut! And there were others. But we found & fixed them all in time. IIRC we had a total of four reported problems. One was a corrupt file header from someone else: logged, referred back to the company sending it. They'd fix it, because if the data couldn't be read we couldn't reimburse them for calls our subscribers had made on their network.
Another was our Dutch subsidiary having failed to implement a fix we'd sent them the year before. They spotted it & put it right while I was looking at the problem. Laugh, log & get back to my book. Ten minutes wasted. The others were equally trivial.
But I digress. Back to the point - I saw an advert for contractors who knew the OS, language, & database that the Yellow Pages system used, for a company that was not named but which was obvious. Urgent requirement! Good rates! A discreet enquiry to a former colleague whose contact details I still had told me that yes, it was still in use, & he was bloody glad he'd left before the clusterfuck which he'd heard was now going on. IIRC nothing had been done to the old system because it would be replaced just in time - but then it got too far behind the rather tight schedule, not helped by the difficulty hiring because of everyone panicking about Y2K . . . .
My turn to laugh.