I'm sure it's not always easy to evaluate that type of situation. Obviously, a woman doesn't have to be physically beat up in order to be a rape victim...just the force of being held down, the fear of getting beat up and/or killed, the verbal threats...all of these things need to be taken into consideration and are all part of this crime. If someone beats someone up, it doesn't necessarily mean they raped the person. If someone is not beat up it doesn't necessarily mean they haven't been raped.
No other witnesses, no physical evidence of force, all just on the "state of mind" of the women?
Lots of people have been tried and convicted of crimes in which there were NO witnesses at all. In a rape case there is always a witness, the victim.