This is Excel 2010.
Under "Format cells/number/text", it reads "Text format cells are treated as text even when a number is in the cell. The cell is displayed exactly as entered." This is not true in my case. I had this number 37820198429287 in a cell whose format was text. It didn't appear as "37820198429287", it appeared as 378202E+13. I double-checked the cell format to make sure it was text. Unlike pure number, which is right adjusted, this one is left adjusted. This cell didn't have a green triangle on its top left corner, which usually appears when a number is stored in text format.
I copied and pasted this cell to several other cells and randomly double-clicked on some of them. The number in them were expanded to show all 14 digits and a green triangle appeared on the top left corner of them.
It seems to me Excel displays numbers stored as text in two different ways. I can't find a reference to this behavior.
Is there a guideline telling when which one will be displayed?