You're very right; I think the one thing I cann say is that the ones that healed weirdly were deep and didnt't close well, well except the car accident wounds. They all magically healed really well. I'll try butterflies, too.
Abrasions tend to heal fairly well, it's only surface layers of skin, it's when you have a laceration that goes in a few layers you can get some really bad scars. Whips and canes can occasionally cause this kind of split, along with more classic means (knives, scalpels, etc).