Here's an interesting question for you: Is Adobe Captivate backward compatible?
This question gets asked quite a lot on the Adobe Captivate Forum and the usual answer is NO. But that's not quite correct.
About Backward and Forward Compatibility
Check the actual definition of the term "backward compatibility here on Wikipedia:
Captivate is BACKWARD compatible but not FORWARD compatible
According to this esteemed source, the fact that most versions of Captivate CAN open files from previous versions (e.g. Captivate 8 can open files from Cp6 or even Cp5) would mean that the application is, by definition, "backward compatible". However, the fact that previous versions of Captivate cannot open or work with current version Captivate files means that those earlier versions are not "forward compatible".
Interestingly, Captivate 6 was so far the only version that seemed to break this rule. It could actually open and edit Captivate 7 files, despite the fact that Adobe did not recommend the practice. However, this respite was short-lived because Cp6 or Cp7 cannot open or edit Cp8 files now.
Beware the one-way SAVE street
Either way, the real issue for most Captivate developers that use different versions is that once you open a file from an earlier version of Cp in a later version of Cp and then SAVE that file, it will no longer be editable in the earlier version from then on.
One potential issue here though is that all Captivate versions since Cp5 now use the CPTX project file format, but there's no way just by looking at the file to determine which Captivate version it relates to.
So, if you DO happen to use a later version of Captivate to open a project file from an earlier version, my recommendation is to make sure you do a SAVE AS and then append the file name with an underscore followed by the Captivate major version number (e.g. MyProjectFile_Cp8.cptx)
This way, if anyone needs to keep editing it with the older version, they still have the original unchanged CPTX as an option. But there is also now a clear indicator for the other file as to which Captivate version will be needed to open it.