This idea has been merged into another idea. To comment or vote on this idea, please visit DTX-I-194 Improve Auditing: add patient index, improve report.
When a user makes an initial entry and then changes the initial entry date, the user ID is not recorded in the audit trail. Article Number 14390: https://hsione.force.com/dentrix/s/article/21539
IMO, this should not be considered 'normal' program behavior and resolving this deficiency should be at the center of your developers radar screen.