If your are referring to the two year aniversary of the collection, it would be 12/2012.That was the date you said it was "assigned". However as stated earlier, that usually is not the date that would initially effect your credit score. If you are talking about the aniversary of the debt, that would be the dofd.
Starting scores 01/ 02/2012 EQ 707 TU 733 EXP 735 (FAKO)
Updated scores 06/15/2013 EQ 761 TU 780 EXP 741 (Fico)
Remember the Three P's: Pay early in Full, Pay on Time, Patience
