We obviously have different view on what forgiveness is about. I see forgiveness as letting someone else off with whatever they did and dispersing of any debt that is created. In Greek we talk about "accommodating them on common ground." From what I have seen this is the worst thing someone can do if the other person is evil.
What you are talking about, in my book, has nothing to do with forgiveness. It has to do with resolving issues that are standing to help resolve emotional responses. If for instance there is a violation or issue of injustice we naturally get angry. So we need resolve the issue in our minds to be able to stop being angry.
We all live in the present all of the time. The most common reason why past issues arise is because someone related to us, who wants to use that past issue to hassle or trouble etc., is using relationship and the mental entanglement there is in relationship to present the idea. People perceive it and think it is their own thinking. Thus they become troubled. The important thing to understand is that ideas are not in business for themselves.
From what you say a person cannot escape being hassled because no matter how much "you let them go" if they present ideas and you don't realize they are just rubbish suggestions you will react. We interact mentally and no amount of letting them go is going to change that.