The pricing plan for the Watson Natural Language Classifier service says "First four training events per month are FREE. Additional training events are $3.00 per training event. Training events are tracked and charged for on a monthly basis". What is meant by training events?? We train the classifier only once when we create it. There is no API available for updating the training data for an existing classifier? Then, what are training events? Also, is this pricing per classifier or for the entire service instance?
You're not charged for adding to the training data in the toolkit, but the data is not available until you create a classifier with that data.
You get 4 training events free per month. Let's say you create a classifier (1 training event), and then add training data 3 times in the month. You also create a classifier each time you add to the training data (3 training events). Finally, each time you create a classifier, you delete the old classifier.
Those 4 "training events" are free. You still have only 1 classifier, so that stays under your free limit.