Well, someone from the Department of Insurance called me and clarified this issue. Apparently I am wrong and Slick and DG are correct. It is not case law but an October 22, 2002 opinion letter.
The pertinent part of the letter: “1) With respect to the payment of simple 2% interest, it is specifically stated that this requirement will become effective and be applicable to all overdue claims arising out of accidents which occur on and after April 5, 2002”
This answers the question.