Sometimes people use terms back and forth and think it is perfectly clear to everyone what is happening or what the correct interpretaton is. I wonder if this is not the case with the DP and the Flex and the term out of the game (line up management tutorial or left the game). This deals with one going in for the other.
Regardless of the term, one means that the DP or the flex is not leaving the game under the substitution rubrics. It is a whole different rubric.
My understanding is the starting DP and Flex can swap back and forth all game long and it has no bearing on re-entry.
