Below are Sec 21A (BOD) & 21B (DC) — Sec 21B clearly mentions about more than one DCs, see highlighted portion, but there is no such provision in Sec 21A. So it is surprising how ICAI did it. They must have taken legal advise as Sec 21A is silent and implemented it as per there requirement, till the time anyone objects and goes to court they will work as per there interpretations. But people can object 2nd bench of BOD may not follow its orders.
21A. Board of Discipline
(1) The Council shall constitute a Board of Discipline consisting of−
(a) a person with experience in law and having knowledge of disciplinary
matters and the profession, to be its presiding officer;
(b) two members one of whom shall be a member of the Council elected by the Council and the other member shall be nominated by the Central Government from amongst the persons of eminence
having experience in the field of law, economics, business, finance or accountancy;
(c) the Director (Discipline) shall function as the Secretary of the Board.
 
21B. Disciplinary Committee
(1) The Council shall constitute a Disciplinary Committee consisting of the President or the
Vice-President of the Council as the Presiding Officer and two members to be elected from
amongst the members of the Council and two members to be nominated by the Central
Government from amongst the persons of eminence having experience in the field of
law, economics, business, finance or accountancy:
Provided that the Council may constitute more Disciplinary Committees as and when it
considers necessary.