There are two levels here.
It is reasonable for the NB to expect new standards (and even old standards that not yet adopted) to be used as inputs to periodic post market activities as referred to in ISO 14971 (Clause 9) and referred to in the directive (Annex X and general post market obligations).
However these are just inputs to analysis, such standard have not reached the status of giving a "presumption of conformity", with formal legal implications if not applied.
A new standard is an important reference and there may be good stuff in there that is worth implementing ahead of any formal recognition. Also the standard might be held up getting harmonized for some particular controversial requirement, but there may be other requirements that are perfectly reasonable to apply without delay, or at least incorporate into the next design upgrade.
But if the NB is saying that a standards automatically represent "state of the art" as soon as they are published, they are stepping over the line.
The minimum requirement is to show that the standard has been reviewed and decision made whether any requirements should be adopted. The record should exist as part of the post market periodic review activity. If the record cannot be found, it is reasonable for a non-conformity to be raised.
The NB may reasonably question the decision in the record, but note they also need "objective evidence" to support a non-conformity. If the above record exists, the correct procedure has been followed, so the non-conformity relates to the engineering or risk based judgement. The evidence should consist of a feasible rationale, incident reports or other information showing that the particular requirement is worth implementing ahead of formal adoption. They cannot broadly or blindly say that all published standards are automatically state of the art.