Short answer: no one knows.

Showrunners have expressed their displeasure, specifically with Netflix, because there is no concrete information. We get bits and pieces from interviews here and there, but none of it is consistent. Some have said viewings within 30 days, others have said viewings within 60 days. Still others have said viewings within 28 days. Neil Gaiman recently said he was told completion rate was a factor for "Sandman," while other showrunners have mentioned how many people start the show but abandon it, tracked even down to the minute that people bail out.

Whatever the case, it's a moving target. A popular show or film one week may not be considered the same the next. "6 Underground was deemed a hit and a sequel was in the works, until suddenly two months later both parts of that statement were untrue. No one knows what changed.

The showrunner on "The Babysitters Club" gave a great, insightful interview that explored how little they were given by Netflix, but hints at how much data Netflix has, which has led to some wild shit. She mentioned an exec told her that, for example, shows that feature X in the first Y minutes are more likely to be completed

Which is complete claptrap, but it shows that a) execs have access to a fuckton of info but b) they don't know what to do with it except to make very broad assumptions. All we really know is that they don't share it with anyone, including the people making content for them.