I suggest soaking the collar in a highly concentrated solution of Oxiclean for a few hours. It's gotten rid of set-in sweat and food stains on shirts I've loved - it might be able to take care of some ink. Attempting that now. I would imagine that sweat and food are easier stains to deal with, just because they're fat and salt and protein based, and thus can be dissolved by enzymes in the detergent once initially worn down by the Oxyclean. Ink is a different beast altogether. Crossing my fingers.