The following link has a small section at the bottom on Backups:
https://bimmercode.app/manual/
The statement "The first time the coding data is read from a control unit a backup is created automatically to restore the original coding data later or to recover in case of an error." is consistent with you getting the backup files after looking at various options.
My empirical observations are that each of the 7 files is from each of the 7 control units you looked at, with the last 6 characters corresponding to which control unit. You can confirm by only looking at only 1 control unit and getting only 1 file.
If you look at all of the control units, then you would get a "full backup". After that, you only have to look at the control unit you want to change to get a "partial" backup.