Not always the case Snappy. My bitch always had enlarged nipples and always had a little milk right up until she was spayed, when they went small. She had never had any pups, neither had she had phantom pregnancies. She had to have tablets to dry up her milk before she was spayed. Apparently this is quite common
No, she was never without some milk right from the age of about 6 months. Admittedly during her season her nipples got even bigger. The vets told me that this is not unusual.