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Message: <blockquote data-quote="Cagu422" data-source="post: 1641445" data-attributes="member: 344292">I am using Excel 2011 on my Mac with Yosemite.  I have a spreadsheet that I modify each month by creating a new sheet with the month's name in a new tab on the bottom and new calculations for each month.  I save the file each time after modifying on an external drive.  Then close the document.  I also make a backup copy on another external drive.  The problem is when I go back and open the document it reverts back to an old version without any of my new modification. It also converts my backup to the old document.  What makes it frustrating is that it doesn't do it all of the time.  Sometimes it works fine. It's unreliable.  Why does it do this, how can I stop it and where can I find the document with the modifications?Thanks</blockquote>