In my opinion two notices one under Sec 73 in case of issues where there is no fraud, wilful misstatement or suppression of facts to evade tax is established and another notice under Sec 74where such intentions are established is perfectly fine. In fact, I feel, that is the intention of these two sections and there is no express bar in issuing two SCN's at the same time. One under Sec 73 and another under Sec 74.
For example an issue relating to 2A vs 3B difference cannot be a part of a notice in a Sec 74 notice along with other issues that involve FWS. However the Department always takes a stand that if one issue in a notice rightly involves ingredients to issue notice under Sec 74 it gives them a license to club all non fraud cases also with such a notice. "Once a thief always a thief " attitude cannot be accepted in GST adjudication. Each issue in the notice should independently pass muster in the notice.
But if the question is as to whether two notices on the same issue can be given by the officer simultaneously, to be on a safe wicket, then, the answer is an emphatic NO.
Even in cases where invocation of two provisions are logically possible in an issue within a particular notice the officer has to ELECT the violation he wants to pursue. He cannot use both issues in a single notice. To take an example in a particular case it might be logically possible to
A. Demand reversal of input tax
B Demand tax on outward supply
Still, the Officer will need to elect what course of action he intends to take when issuing a notice. It is alright for him to issue another notice if the proceedings in the first notice were finally concluded without actual payment of taxes.
To make this more clear let us assume officer issued SCN demanding reversal of IPT and it is possible that he dropped such demand in adjudication. It is also possible that an Appellate Authority struck down such IPT reversal in Appeal. Then it is perfectly possible for the Proper Officer to issue another SCN demanding output tax provided the time period etc permits him to do so.
If a tax payer submits himself to illegal proceedings without objection he does it on his own peril. For example we routinely find issues like Late fee not paid, interest on late payment of taxes not discharged , 2A vs 3B etc in Sec 74 notices.