When the Download button is clicked on a document in the document library, the Used Count increases.
But Used Count does not increase when Download button is clicked in the Preview window of the document.
Karthik Dev from product team requested me to raise S4 for this. Karthik suggested that the Used Count should increase when this download button is also clicked.
Reference ticket -
https://responsiveio.zendesk.com/agent/tickets/61876