There is indeed a distinction to be made to the intrinsic risk linked to activated carbon itself (in principle independent of origin, though pore size can vary) (“catalyst” for nitrosation as described in literature and cited discussions above (Padhye 2010 and Padhye 2011)) Nitrosamines Risk in Pharmaceutical Waters - Risk Assessment Strategy / Tools & Technology - Nitrosamines Exchange (usp.org)
and cross-contamination risks which can vary across suppliers as their processes for treating activated carbon can differ (questionnaires are needed, but are also useful to rule out this scenario - whereas the catalyst role is more intrinsic (though pH plays a role)). It is known that nitric acid washes to activated carbon can be done by some suppliers for washing away impurities and modulating physical properties of the activated carbon, though it is not standard (and other acids can be considered as well). It will really dependent on why you need activated carbon in the process (what needs to be removed? if it is heavy metal removal: already more likely nitric acid pretreatment) and thus what type of AC you need, impacting how it is pretreated by the AC supplier if tailored AC selection was done.
When activated carbon treatment is late stage, vulnerable amines are present and targeted nitrosamines are well-soluble in the used solvent and unlikely to be fully retained on the activated carbon, then looking deeper into activated carbon impact on the risk is not a bad idea. Practical limitation could be the collaboration between AC, API and DP supplier this could require to maximize expertise and exchange.
API suppliers dealing with vulnerable amines and selecting new sources of AC (especially when needing to select nitric acid washed sources) should probably consider nitrosamine impact already in the design phase and conduct some stress testing with the vulnerable amine in relevant solvents and pH to check its compatibility with the AC from a nitrosamine formation perspective.
Some examples of nitric acid treatment:
Preparation of nitric acid modified powder activated carbon to remove trace amount of Ni(II) in aqueous solution | Water Science & Technology | IWA Publishing (iwaponline.com)
Effect of nitric acid treatment on the pitch properties and preparation of activated carbon | Carbon Letters (springer.com)
Effect of Nitric Acid Pretreatment on the Properties of Activated Carbon and Supported Palladium Catalysts | Industrial & Engineering Chemistry Research (acs.org)
Tailoring the Surface Chemistry of Activated Carbon by Nitric Acid: Study Using Response Surface Method | Bulletin of the Chemical Society of Japan | Oxford Academic (oup.com)