Yes, did they teach you how to use what's left in the pen before starting with a new vial?
Yes. Right now my dosage is at 300 a night and I have 600 and 900 size cartridges. It's all nice even multiples, so it should be fairly easy between dosages.
My dose was also 300 a night but I had the 300 cartridges. I always had at least 75 left over in the cartridges after each dose. REs office gave me a heads up about this saying that it's normal, not to freak out, and it's a bonus. Have read this for others as well!