When I do the forgiveness work, I try to take what you call the personal perspective of the one who hurt me. Yet, how much of this work must be factual rather than speculative?
As you say, we ask people who forgive to take what I call the personal, global, and cosmic perspectives. The personal perspective deals with facts, to the best of your ability to gather those facts about how the other person was raised and the challenges faced in life. If you have no knowledge of the other person’s past, then I recommend that you move to the global perspective in which you begin to see the common humanity that both of you share. You do not need to know precise details of that person’s history to know that you both: 1) have unique DNA, making both of you special and unique; 2) must have adequate nutrition to be healthy; 3) will bleed if cut; and, as one more example, 4) will both die someday. Seeing your common humanity may aid you in softening your heart toward the person, not because of what happened, but in spite of this.