title: Some but not all Excel numbers show as a date
body: <p>I have a big .xls file. Some numbers show as a date.<br/>
  31.08 shows as 31.aug<br/>
  31.13 shows as 31.13 (that is what i want all columns to be)<br/>
  When I reformat 31.aug to number it shows as 40768,00 
  I have found no ways to convert 31.aug to 31.08 as a number. All I am able to do is to reformat 31.aug as d.mm and then it shows as 31.08 and when I try to reformat it from 31.08 to number it shows as 40768,00. No way to cheat Excel using different types of cell formats.</p>