On a few occasions I've inserted the refill syringe into a new cartridge and it goes ALL-THE-WAY-IN. Generally it seems to happen only when I've inserted the syringe near the edge of the "Insulin Fill Port." There is literally no resistance.
But I haven't filled it that way. I remove the syringe and insert it near the center of the "Insulin Fill Port" until the syringe meets resistance.
Am I doing any damage to the new cartridge when this happens? I haven't noticed any odd behavior from the pump or any effects on my blood sugar. In that sense it's a 'no harm, no foul' situation, but I wonder . . .