Numbers file keeps reverting to old version

I use Numbers (Version 3.5.2) on my MacBook Pro running (Yosemite 10.10.2) and also on my iPad air (running iOS 8.1.3) and iPhone 6 (running iOS 8.1.3). I have a file that I use to keep track of grades that is used across all three devices. In the last month the file keeps reverting back to an old version of the file. After this happens I can go into Numbers on Mac and Select "Revert to..." and select the correct version of the file. I did this yesterday and deliberately reverted to the correct version on the Mac and saved, then opened the iPad, made sure it had the correct version, made a minor change and closed the file. I then opened on the iPhone made sure it was the correct version, made a minor change and saved. I then reopened on the Mac it was the correct version and included the minor changes made on the iPad and iPhone. I saved and then closed the file. Today when I open the file on my Mac, it is back to a version that is over a month old. I again used the "Revert to.." command and was able to get back to the correct version of the file from yesterday. I can't figure out why it keeps reverting to an old version. At first I thought it was pulling in an old version from the iPad or iPhone, but after the experiment yesterday that does not seem likely. Has anyone else had this problem? It is making me seriously question the use of Numbers with documents in the cloud as I can not be certain that the data in the file is correct.

Thanks for any suggestions.