What I do, is when I update the software to the newer version (eg, R71) I quickly rename the old copy to Construct2 Old, and then install it, When it prompts you to uninstall the older version it finds say no, It will make the newer version the default but you still have the older version just in case, so then test your projects on the new version if they work delete the old..
Or you could be normal and if there is a problem go to the release archives and download the copy it worked on! :D