As it turns out, there is a formula. It’s based on two of the three factors that exempt teams from preseason Hard Knocks.
For the preseason Hard Knocks, teams get a pass if: (1) they have a new head coach; (2) they’ve done it within the past 10 years; and (3) they’ve been to the playoffs in any of the prior two seasons.
For in-season Hard Knocks, the league uses the first two categories, but not the third.
It’s unclear whether participating in preseason Hard Knocks during the prior 10 years applies to in-season Hard Knocks. For the Dolphins, it doesn’t matter; they did preseason Hard Knocks in 2012, eleven years ago.