The date provided in your skill assessment result letter is the date you have met the ACS requirements.
Your experience between January 2008 to February 2012 has been considered in your skill assessment application in determining the outcome of your application.
As your Bachelor was not relevant to the nominated occupation you were required to demonstrate 4 years’ experience which was completed in February 2012.
February 2012 is the date you met the ACS requirements and is the date in which you have been deemed to reach the appropriate skilled level for your nominated occupation.