This story has also been told here previously but worth repeating because there's a moral in it.
Client had 2 Sparc based systems running their accounting. One was new enough to have run the Y2K prepared version of the application, the other, a warm standby wasn't. (In the course of testing I discovered that the warm standby not only wasn't new enough, it also wasn't a warm standby because the overnight copy was failing due to lack of time. As this was previously unknown it wasn't a factor in the decision making.)
They decided to replace them with a pair of SCO boxes running the latest version. My job was to set these up and look after user testing. The bean-counters ran their acceptance tests and pronounced them OK. The planned cut-over was between Christmas & New Year when the plant was shut down.
At the last minute, despite dire warnings, bean-counters completely forbade any replacement before they'd completed their year-end bean-juggling on the old system which would take them up to mid-January. If we'd had a bit more warning we could have insisted on their testing the year-end on the new boxes but, of course, they hadn't done that.
Inevitably there were problems which required the A/C package vendors dialling in, sometimes multiple times a day, to sort out the mess until we were allowed to switch over.
The moral of the story: for those who insisted that all preparation was just unnecessary freeloading and panicking, those who chose to deliberately run on a nonY2K-proofed system suffered real on-going consequences.