Are you running Mountain Lion (Mac OSX 10.8.x)? If so, and you are using Pages, you should be aware that Apple has implemented a new auto-save feature for its software (and other software that has been written to comply). The very good news is that you can retrieve prior states of your document. The bad news is that the feature makes it easy to modify your work inadvertently by saving your changes without your knowledge. I don't think Apple has it quite right yet. In any event, research OS 10.8 auto-save and see if this might be your problem.