Re: Upgrading from 1.9.5 to 2.3

'Upgrade' is supposed to mean that you carry _all_ the data from the previous version, i.e. users, courses, all user interactions in those courses, .... This is the documentation:
- http://docs.moodle.org/19/en/Upgrading_to_Moodle_1.9
- http://docs.moodle.org/22/en/Upgrading_to_Moodle_2.2
- http://docs.moodle.org/23/en/Upgrading_to_Moodle_2.3

If you want a fresh start, course export/import might be better:
- http://docs.moodle.org/19/en/Course_backup
- http://docs.moodle.org/22/en/Course_restore
- http://docs.moodle.org/22/en/Course_backup
- http://docs.moodle.org/23/en/Course_restore

I have no idea of the compatibility amoung the various backup versions. Hope somebody else could help.