by Emma Richardson.
More importantly, were you taking backups of the courses in question?
If not, you will need to reset up the moodle 3.1 version, then take backups of the courses to import into the 4.3 version...
If you were taking backups, were they being sent to a specific folder or saved in the course area? Hopefully you can search your moodledata folder for files of .mbz type and find them...