I would like to know the opinion of experts on the following assuming notice is on the basis of 2A and 3B difference
I feel in such situations it is necessary to look at the allegations made by the department. Most probably they will invoke violation of Sec 16(2)(c) and the evidence canvassed being difference between 2A and 3B.
In such cases you can challenge the SCN on the ground that there is no violation of Sec 16(2)(c) and SCN was issued on the basis of inadequate investigation , assumptions etc and if the department were alleging violation of supplier having failed to pay tax the department should have identified the supplier and must have tried to collect tax from him in the first instance...
In my opinion the allegation in SCN by department should be claiming credit of a non existing supply under Sec 16(2)(b) and the eligibility to credit has been lost due to Sec 16(4) time limit.
But generally they invoke violation of Sec 16(2)(c) in many such cases because they wont be able to identify the exact cause easily without a thorough reconciliation which is very unlikely.