Special Committee is very rare. We had one In our congregation in the 90's. Many of the Friends were complaining about the Elder Body, 4 out of 6 connected by Family, not respecting the Disfellowshipping arrangement when it to shunning DF'd family members. The CO called the Branch and was told to appoint 3 of the most experienced Elders of the Circuit and give them the Power to make any necessary changes to the Elder Body as they saw fit to keep the Congregation from splitting up. The result was 5 Elders deleted and 2 Elders (pure company men) brought in from other Congregations, I was one of those brought in.
3 of those 5 never served again. 1 was later DF'd himself and the other is currently Serving.
I friend from a congregation in Miami, FL(Kings Bay), said the same thing happened there around 2000.
An Appeals Committee, is appointed by the CO to hear the plea from someone who thinks an error in Jugdement was made on them being Disfellowshipped. The Appeal Committee can overturn the original Committees decision if they felt an error was made. I have served on an Appeal Committee.