Can the latest version open files created in older versions of KaleidaGraph?

As long as the files are intact, the current version can always open files created in older versions of KaleidaGraph.

If you need to open the files to an older version, version 5 allows you to save plot and layout files in a v4.0 or v4.5 format. The data files can be saved in a v4.x format (the file formats did not change from v4.0/v4.1 to v4.5).