> "I store all dates in spreadsheets in ISO format"
As in SQL, the application’s native date format (which is usually a number with appropriate format) would be the natural choice and a YYYY-MM-DD string would be a distant second. ISO (presumably, 8601) format is too broad, and admits of a mix of formats that are not simply sortable (quick, which is first 2021-W14-2 or 2021-04-07?).
Eh, when people say ISO they mostly mean YYYY-MM-DD.
If a date is going to be string prepended to something else, or if the spreadsheet is going to be exported to CSV, or parsed by some tool, then storing dates in YYYY-MM-DD can be a very justifiable thing to do in a spreadsheet.
Also Excel likes to format dates using the system locale, which is, well, stupid. So I have to enter YYYY-MM-DD as a custom format anyway, or change the locale on the column to China. (Or Cherokee, who apparently also properly format their dates!)
(Also Excel is smart enough if you set a column as YYYY-MM-DD custom format, it'll let you use all the date based pivot table stuff as expected)
As in SQL, the application’s native date format (which is usually a number with appropriate format) would be the natural choice and a YYYY-MM-DD string would be a distant second. ISO (presumably, 8601) format is too broad, and admits of a mix of formats that are not simply sortable (quick, which is first 2021-W14-2 or 2021-04-07?).