I too was stabbed in grade school; twice actually, in the same hand. I think both times for pestering girls as they were writing, lol. I guess I deserved it.
Both left visible gray marks under the healed skin...one on a finger and the other in the soft tissue between my thumb and index finger. Years later, in my 30s, I was handling some super strong magnets and felt tugging on the tissue next to my thumb, indeed that magnet was pulling strongly on that piece of embedded graphite.
I thought that was strange because either the graphite had impurities of iron in it or my body had accumulated iron around it.
Some years later I would develop random knuckle pain in a couple of the nearby fingers. I was skeptical that this foreign object was to blame...but I convinced a doctor to do some minor in-office surgery to remove it.
The doctor made an incision and using forceps tried to find and pull it out. He couldn't find it (which he initially warned me about and suggested ultrasound guidance) and asked me to get out my magnet and pull the object up...his forceps immediately snapped to the magnet, I didn't flinch but was laughing internally. He grabbed the object, which was probably half the size of a sesame seed...much smaller than what he was expecting based on the amount of tissue that was being pulled up by the magnet.
Months would pass and I no longer had pain in those knuckles, that was probably 5 years ago. The other stab mark, which is on a different finger, never caused any issues.
The nurse afterwards said, "I cannot believe you did that." I chuckled.
I can now say that I've assisted in my own surgery ;-)