Casual vacancy of auditor before audit

HI All,

I need you advice in the following case study:

There is a company A, whose old auditor(MR. O) resigned before the audit. In this case the company decided and appointed a new auditor (Mr N).The audit of the Comapny is done by the Mr. N .Hence it is the case of casual vacancy of the auditor. Further in above case Mr O resigned on 01.08.2016 and Mr N signed balance sheet on 05.09.2016. AGM is held on 30.09.2016.

WHat Law states?

Any casual vacancy in the office of a Statutory auditor shall— in the case of a company other than a company whose accounts are subject to audit by an auditor appointed by the Comptroller and Auditor-General of India, be filled by the Board of Directors within thirty days, but if such casual vacancy is as a result of the resignation of an auditor, such appointment shall also be approved by the company at a general meeting convened within three months of the recommendation of the Board and he shall hold the office till the conclusion of the next annual general meeting;

Now as per Section 139(8) any casual vacancy in the office of Auditor due to resignation of auditor shall be filed by Board of Directors within 30 days and such appointment by Board
shall also be approved by the Company at a general Meeting convened within 3 month of the recommendation of the Board.

following are the questions need to be answered:
a) Is it necessary to hold EGM when the AGM fall within the 90 days limit? Or AGM is enough.
b) what all forms need to be filed for casual vacancy and annual filing?
c) Do we need to filed 2 ADT-1, one for casual vacancy and other for the block of 5 year ? Or 1 form is enough.
d) If one ADT-1 need to be filed how the drafting for appointment will be done.

Thanks
Poonam Kayal
PCS