It was still not excluding the rows in Data where there is at least one Note added in the last 3 months (those have recent activities and not a concern), So for Data 1 there is a Note added on 15-03-12 which is in the last 3 months.
I figure out that I needed to move this WHERE statement:
DATESUIVI < Add_months(SYSDATE, -3)
From the inside SELECT to the OUTSIDE SELECT at the end.
Now I am getting the expected results for real :D