Was an elder for 20 years, Never heard of it.
DFs dont get overturned.
Procedure is:
Local JC makes the determination.
If the publisher disagrees with the outcome - there can be an Appeal.
A JC with more from outside the Congregation usually with experience reviews the case to see if mistakes were made, and upholds the DF or no.
If publisher still disagrees saying something was done wrong - it can be appealed to the Brach (FYI almost know one knows this).
But when someone is DFed - there is no other mechanism but doing your time and coming to meetings bla bla bla, for the verdict to change.