title: Excel filter groups some dates but not others
body: <p>This may be a dumb question with an obvious answer but i can not find or figure out a solution. So I have an excel sheet with 5 tabs, each tab with different data. I've added a filter on the tabs and with some of the date fields it groups by date (you can choose year and month) when you select the drop down. But on others it doesn't.  How can i get it to give this grouping option on all of the dates????</p>
  
  <p>Thanks</p>