I don't think Excel ever destroys the underlying data. It simply layers formatting over it. One can override by specifying custom formatting, or opt out by selecting all cells and setting their format to text.
Once the data is in the cell, changing cell formatting is a nondestructive visual layer. But while inputting data, cell formatting changes the interpretation of the input, which is destructive.
The article describes in some detail how inputting SEPT2 in a cell with default formatting displays 9/2/2016, but is stored as 42615 (which you get if you later change the cell to text formatting).
The article describes in some detail how inputting SEPT2 in a cell with default formatting displays 9/2/2016, but is stored as 42615 (which you get if you later change the cell to text formatting).