Excel 2011 not opening newest document

[Cagu422]

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

 

[Cagu422]

I have determined that for some reason Excel thinks the older version is the newest document version. I found this out by trying save a new back up and got a message saying that " a newer item named ***** with extension .xlsx already exists in this location. Do you want to replace it with the older version?"

Is there a setting wrong somewhere? I have looked in the preferences and properties and can't see anything. This is frustrating because I feel I can't trust Excel. I am used to solving software / computer issues but this one has me crazy.

Thanks again.

 

[sullij]

I'd suggest that you choose "save as" when you go to save. You'll see the various formats and will be sure you are consistant.

 

[Cagu422]

I looked at all of the files and they are all XLSX versions. I did Save As also and it goes to XLSX. How does Excel set it's modified time? Or is that based on a setting on the Mac?