Sir, Can you please give reference of the section number? I wasn’t able to find the same.
Requirement to inform auditor and ROC within 15 days after appointment is given as proviso to Sec 139(1) , hence it appears that this requirement is only for auditor appointed under 139(1) i.e appointment at AGM.
But if you read form ADT-1 and its instructions, it is specified that details about casual vacancy are also required, that means this form is also applicable for casual vacancy.
in short it will be required for all appointments after first auditor whether in AGM or whether casual vacancy