Sarah, if it helps, this is how to determine the version of the backup file, which is basically a tarball (TAR/GZ archive)

• Open the XXXXXX.MBZ backup file in 7-Zip, WinRAR or similar
• Extract the single file within
• rename the single file within to XXXXX.TAR
• Open the TAR file with 7-Zip, WinRAR or similar
• Read the file 'Moodle-backup.xml'

You'll be presented with a bunch of useful info on the backup, including version info. 

regards, Andrew