Summer67 makes a good point here.
It gave me some relief - to know that it was not me who had elicited this behaviour all by myself.
Many of us will have been told that we were the cause of the behaviours and if that is something that remains a belief on our part, it can be damaging to our self esteem which is likely already low and thus affect our healing. If contacting an ex partner in the early stages of detaching helps to put that to rest and prevent the cycle of self blame and guilt, then that can be a positive in my opinion.
It also depends on the situation (how extreme the behaviour was being a key thing to consider) and whether you can be confident that there is no chance of there being negative repercussions from it. It is important to be wary of smear campaigns that could be damaging or escalation in destructive behaviour, and having certainty that there is no ongoing r/s between these people and the ex is going to be a factor in making decisions about this.
There also comes a point where we need to see it all for what it is, and by learning enough about BPD we can see that blame and projection are common, so this gives us the chance to let go of these things without the need to investigate further. It is a personal decision, and I would encourage anyone considering this to think it through carefully, maybe discuss it with others first to get an outside view and to always
safeguard themselves against any backlash if they decide to go ahead.
Personally, I had no wish to have any connection to anyone in his life, past or present, as that to me was maintaining a link to him that I simply didn't want in my bid to move forwards. So I did not contact any of the exes. Sometimes it can be worth considering whether contacting others to discuss an ex is in an indirect way keeping that person in our lives rather than directing our attention to ourselves. Just food for thought.
Love and light x