Right. If the communication is just routine regulatory back and forth, then it does not prove approval is coming.
But if the claim is that MHRA gave NWBO feedback strong enough for management to know approval is coming, then that starts looking like material nonpublic information.
It does not need to be on official letterhead to be material. Materiality depends on the substance of the information. If a reasonable investor would consider it important, especially in a company where approval is the central value event, then it is hard to wave it away as immaterial just because the formal approval letter has not been issued.
So the argument cannot have it both ways. Either it is routine confidential review discussion, in which case it does not indicate approval is coming, or it is a definitive positive signal, in which case materiality and insider information become real issues.