What is the best way to maintain consistency between versions (ie for different countries or languages)?

When dealing with different versions of the same catalog (for example, Canadian, US, and European versions with different pricing) working with multiple versions of the same files can get confusing.  Something might get updated in one or two of the three versions when it should be the same in all three etc. To avoid these issues, you can use InDesign and utilize the program's "layers" function. The "fixed" content (which is the same in all versions) will be on the bottom layer. The content specific to each version can be on different layers. Every layer can have the information specific to one of the regions. This way, there is only one master file to maintain. Edits will only need to be made once. When exporting one version, you can hide layers you don't need. The fixed content is always showing, ensuring there will not be unintentional differences among versions.