Whenever someone opts into a standard keyword we check to see if that number is already opted into any emergency keyword associated with that account. If it isn't then we add it to the emergency list; the logic behind it is that if someone is in your service area - which would be the only reason they would opt-in to the standard keyword - then we would want them on the emergency keyword list in order to keep it as complete as possible for the utility.
The reason that you may see additional opt-ins for a particular month is that our system adds a couple dozen or so per night for each customer in order to get all of the existing numbers already opted into keywords into the emergency keywords without totally tying up the system.
There's no charge for this and no fees are applied for the automated updating. It's just another service we provide to insure that our customers can do the best thing for their members.