Separating input and output KPIs is a concept rarely used in content marketing. For companies that are in the process of discovering content marketing, the quantity of content translates to the number of experiments you can make. And I say this because these types correspond with the three possible goals you can directly achieve with content marketing (read my article on marketing goals for more details). Sales are too complex a phenomenon to attribute to one marketing tactic, even if content marketing is your only tactic. Content marketing affects many aspects of marketing (the whole marketing funnel), so tracking how many sales you got from content would be shortsighted.