Date Formatting in Excel

[Michael Levy]

No matter how many times I try and designate a Date format different than the default the newly designated format only works for one entry. I am using FORMAT>CELL>NUMBER>DATE to set the format. The chosen format yyyy-mm-dd is not noted as any of the ones that would conflict with the OS. In any case I also changed the setting of the OS to agree. The dates are just a large number of individual entries in a a column of cells that will be used for a sort routine.

[#2]

Michael, can you share some sample data or a small print screen?
I assume your cells are not different formats of dates, but in fact text, So we'll need some sample data to verify.
For example, if I have below 2 values in A1 and A2, if I will try to format column A as short date or any other custom format, Excel will only be able to format value in A2 because it can match month to month, date to date etc.
21/10/2018
10/21/2018

[#3]

Here is Screen Shot. Dates are in the correct form as I have manually changed them one by one. This is about as simple as it gets, but I don’t know how to fix it. If I understand you I have to somehow indicate to Excel, in advance, that what is being entered is a date. If I don’t specify that, Excel will recognize it as a date after entry and default to the standard form.

[#4]

Hi Michael,

First, some of your entries are not in correct date form (e.g. 1997--9-26, 1994-!-30, etc). 

Dates in correct form, but entered as text, you may convert to dates by selecting Dates column, on ribbon Data->Text to Columns and on third step of the wizard select Date and YMD