You mean those that you couldn't get it from, not won't right? "Won't" sounds like you decided not to go ahead, that's all.
I've got a couple. Tina from Broadway. Got very far with her, every sesh was full on DATY until I looked like I had a bad cold with my face covered in snot, but always a very clear line drawn.
Same goes for Hera from SS.
Those 2 experiences actually changed me into someone who would never try to pursue FS from an ML if it is not offered on the first visit, no matter how hot she is. I just find it to be such a chore making myself go back to a girl who I know will probably not give me what I need at that time. I'd still go back if I was just after an HJ though.