How do writers know whether 1st edition of books are still sold in the market?

August 16, 2017 7:10am CST
In case of many books, the 2nd edition of the Books are published. The Publication Houses ask the writers that first edition of the Book are totally sold and so the 2nd edition with enhanced material is required to be published. Writers give the added materials. Once the 2nd edition is circulated, how do writers know that more copies of the first edition are still sold in the market by the publisher or not?
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