Invoice showing in GSTR2A (date filed 12 August) but not in GSTR2B (Date generated 14 August)

So my vendor (MTNL) filed its GSTR 1 on 12th August. And MTNL bill (invoice) is showing in my GSTR2A.

My GSTR 2B is generated on 14th August. But it is not showing the MTNL bill in it.

Why is it so?

It appears that GSTR 2B is generated based on the last date of GSTR 1 i.e. 11th August. And not based on the date GSTR 2B itself is generated i.e. 14th August.

But on the other end if vendor files IFF return (last date 13th August) then it will be accepted in GSTR 2B.

So this is crazy logic.

An invoice added on 12th is not accepted because it goes in GSTR 1.

But invoice added on 13th is accepted because it goes in IFF.

Am I correct? Is this the reason why MTNL invoice is not showing in my GSTR 2B?

Or should I contact GSTIN to rectify the error?

Thank you.