I would rather not hang the auditor just yet.
Hopefully the OPs documented information makes clear which drawings need or not approval. If that is not specified in the system, then there’s certainly an unidentified risk, or an opportunity for improvement, perhaps even a nonconformity.
Many drawing templates have a “checked” or “approved” box that, if left empty, may imply that a check or an approval is missing rather than simply not required. I can see it leading to confusion in suppliers, clients or consultants. I think it may be good practice to mark such box with N/R if such check is not required. This way no one can be confused as the auditor may have been.
So, in summary, at least two small improvements can come of this: (1) clarification in the system of which drawings need approval, and (2) a documented distinction between drawings where approval is not required and those where approval has not yet been done.