It is not known what exactly you mean. You write about copying and in the example you have references to cells with dates, which is quite different. Excel uses different methods of writing the dates. If a date is identified as a date (number), its format is determined by the cell format. In your example, the system formatting is set, so what exactly is it for you - it is not known, because everyone who opens your file sees their own system format.
The formula you used combines the contents of two date cells into one text. Unfortunately, this cannot be done in a universal way. If you reference a formatted cell in a text expression, the formatting disappears. They must be specified explicitly with the TEXT function. But this will be the formatting determined by a specific format code, and what is yours - we do not know. If you have dates with dots then you should use something like this:
If you use a different date format, use your own format. However, the result will not match if you change the format in the source cells.
