Imagine this... Four DXpeditions from four different countries from near the same area at the same time. And every DXer in the world needs all four for ATNOs. Does that sound like a recipe for disaster or what?
This happened in Oct 2010, with PJ2, PJ4, PJ5, and PJ7. The teams knew ahead of time this could turn out to be a major success that would make many DXers happy, but they realized this effort had the potential to be the biggest cluster **** in DX history. With careful planning, execution, and coordination between the teams, I don't recall a single incident of them stepping on each other. Kudos to the teams for a job well done.
As for DXpeditions listening where others are transmitting, this has probably been going on since operating split was invented. "Hey lid, he's working split," when the caller is actually trying to work another station. They usually seem to figure it out and correct the situation. As that famous shrimp boat captain Forrest Gump once said, "**** Happens" or "c'est la vie."