This wouldn't have any meaning in England because a 'prescription' is a document from a medical doctor (or optometrist, or dentist) which states what specific medication is required for a patient. You cannot prescribe in advance because you don't know what is wrong with them. Therefore the concept of preparing something beforhand which isn't then going to be used doesn't exist.
In America, and probably other Countries, 'prescriptions' might better be described as 'remedies'. So for instance you might have a 'prescription' for a rash on your arm. This might be a common thing (eg poison ivy), and chemists (or pharmacists, or whatever you call someone who sells medication in your own Country) can stock up on regular 'prescriptions'. If the remedy then goes out of fashion, or is replaced by something better, then the seller may wish to sell them off cheaply as 'discontinued prescriptions', that is, they are longer manufacturered (manufacture of them has been discontinued).