Return filing before registration required or not

My client was registered in vat. But he forget to migrate into gst regime.

Now on he gets his registration in gst in March month.
Now my query is whether he is required to file return for july to sept and oct to dec
,or
I can show all sales made during July to march in jan to March quarter. Bcz during 2nd n 3rd quarter gst registration certificate was not issued to him.

My clients opt for composition scheme.