Does the ruling of choosing when in doubt about the emission of semen or other fluids also apply to one who doubts what has been emitted from either of the two private parts (semen or faeces, menstruation or wound blood), or is it specific only to the emission of fluid from the front private part?

Shafi'i jurists are of the view that whoever doubts whether what has exited from him is manī (sperm/seminal fluid) or madhī (pre-seminal fluid), he may choose between them, assigning to it the ruling of one of them. This reasoning applies to doubt concerning whether what has exited is manī or something that has exited from the anus. As for one who doubts whether what she saw is menstrual blood or not, the default is that she has not menstruated until she is certain of seeing menstrual blood.