Nielsen BookScan
...that before Nielsen BookScan began tracking point of sale data at bookstores, nobody knew how many copies were being sold of literary works that were published by multiple publishers and had entered the public domain?
...that before <b id="mwC78"><a class="mw-redirect" href="./Nielsen_BookScan" id="mwC8A" rel="mw:WikiLink" title="Nielsen BookScan">Nielsen BookScan</a></b> began tracking <a href="./Point_of_sale" id="mwC8E" rel="mw:WikiLink" title="Point of sale">point of sale</a> data at bookstores, nobody knew how many copies were being sold of <a href="./Literature" id="mwC8I" rel="mw:WikiLink" title="Literature">literary works</a> that were published by multiple publishers and had entered the <a href="./Public_domain" id="mwC8M" rel="mw:WikiLink" title="Public domain">public domain</a>?