The century date problem as it was known before Y2K was first described in the 1950s but people assumed it would be a moot point long before it was a problem.
When some of those mainframes were still in use in the 70s it was brought up again but nothing was done because it was assumed that it would be a moot point long before it was a problem.
When some of those mainframes or software were still in use (banks, oil companies, the IRS, etc) in the 90s it was finally seen a as a problem and cost billions of dollars to fix.
Then it happened again in 2020 because it turns out that the fix was to kick the can down the road again.
Finally learning some lessons!
The century date problem as it was known before Y2K was first described in the 1950s but people assumed it would be a moot point long before it was a problem.
When some of those mainframes were still in use in the 70s it was brought up again but nothing was done because it was assumed that it would be a moot point long before it was a problem.
When some of those mainframes or software were still in use (banks, oil companies, the IRS, etc) in the 90s it was finally seen a as a problem and cost billions of dollars to fix.
Then it happened again in 2020 because it turns out that the fix was to kick the can down the road again.