As these large numbers are NOT going to be used in a calculation, the issue is easily resolved, by simply formatting the cell to Text before entering the numbers. Here's how to do it:
- Select the cells of the columns where the numbers will be stored.
- On the Home tab, select the Number Format drop-down.
- Scroll all the way to the bottom of the list and select Text.
- Enter required numbers as usual.
A note to remember: if you copy and paste numbers from a different area to these formatted cells, you'll need to use Paste Special Values or Paste as Text to retain the Text format in the cells. However, if used correctly, this will enable you to use more than 15 digits in Excel.