There is a peculiarity of MS Excel, that it has inherited from Lotus 1-2-3, that it treats year 1900 as leap. [1] This makes dates prior to 1900-03-01 different in Excel and Calc (see e.g. bug 155098). The [1] shows how MS has documented this special treatment; because it's important in some cases, Google has documented their handling of year 1900 in [2]. We also need to have a similar note, maybe on the page for Calc's Calculate options [3], ISLEAPYEAR function [4], number format codes [5], and who knows where else :-D [1] https://learn.microsoft.com/en-US/office/troubleshoot/excel/wrongly-assumes-1900-is-leap-year [2] https://developers.google.com/sheets/api/guides/formats [3] https://help.libreoffice.org/7.5/en-US/text/shared/optionen/01060500.html [4] https://help.libreoffice.org/7.5/en-US/text/scalc/01/04060111.html?DbPAR=CALC#bm_id3149566 [5] https://help.libreoffice.org/7.5/en-US/text/shared/01/05020301.html?&DbPAR=CALC&System=WIN
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/18bf37d1dadbdd5631b8c3a60d3385038513f3df tdf#155100 LibreOffice treats 1900 as a common year, not leap
Olivier and Mike, any follow-ups or OK to close?