> Is Stuntz responsible for the release of those sources?

That's the core question here I'd say. I'm still caught between the reasoning from the old MorphZone thread (i.e. they received the 2006 MUI4 source code in a legal way) and the new (at least for me) claims from KennyR here (i.e. they didn't get any MUI4 source code and instead reverse-engineered MUI4).
It would be helpful if the MorphOS team publicly communicated which of the two (or a third option maybe?) represents the truth.