esperanto_story1-8, Exercise 1: How many speakers?

Model answer (check the figures):

"Nobody knows exactly how many people speak Esperanto. Published estimates run from tens of thousands of active speakers to a couple of million people with some knowledge, and the figure depends on the definition. There is no census, 'speaking' covers everything from a few phrases to fluency, and association membership counts only those who join. Better evidence would be a survey that defines its terms and samples learners, exam entries, congress attendance over time, and independent data from courses, each quoted with a date."

Care: name who made each estimate and how. Do not choose one number because it suits your argument.