Set the Flux Capacitor for 12/30/1899
https://thedailywtf.com/articles/set-the-flux-capacitor-for-12-30-1899 [thedailywtf.com]
2019-02-05 20:38
Until Microsoft comes back into the picture, anyway. As previously stated, what users really want is Excel, but Excel doesn’t exist yet. So you need to make it. Lotus 1-2-3 owns the spreadsheet space, so Microsoft is actually the plucky upstart here, and like all plucky upstarts, they have to start out by being compatible with the established product. Excel needs to be able to handle Lotus files. And that means it needs to handle Lotus dates. So it replicates the Lotus behavior, down to thinking 1900 is a leap year.
Also: https://blogs.msdn.microsoft.com/ericlippert/2003/09/16/erics-complete-guide-to-vt_date/
Also: https://www.joelonsoftware.com/2006/06/16/my-first-billg-review/