You're right! They never go back to studying the plants...unless you drag them to one about 4 or 5 times a day. I've gotten many Master Doctors in this way, and, once you get them over a certain Adept level, some will become Master Doctors on their own. Some get it through age, and some through heritage. I've had one as young as 16, and most of my older doctors are Masters. It's work, but it can be done.