If you are a code official or representing a code official, I recommend avoiding suggesting anything to a plan review applicant. Using Sifu's situation as an example, if the applicant did as Sifu suggested, and later the building burned down, and the owner sued the design professional, the design professional could attempt to push the blame on the AHJ with the defense that they had originally submitted a more fire-resistant building. Of course, the AHJ would counter the argument by stating the design professional had ultimate control over what is submitted and that what was submitted was perfectly legal. The point is, regardless of who is right or wrong, the AHJ would never have been brought into the situation had they left their suggestions to themselves.
As a code consultant, I try to find the path of least resistance, as mentioned above. However, some circumstances may take the design team down a different path that may not be obvious to others. For example, if the owner wants to expand the building in the future eventually, I present a few options, such as an exterior wall constructed as a fire wall with a lower construction type, a standard exterior wall with a higher construction type, or a future fire wall (requires demolition or double fire wall) with a lower construction type.
I have determined the construction type of an existing building (when the AHJ does not have a record and the drawings do not show a construction type) using the record drawings for the original construction, physical inspection of the existing building, or a combination of both. I have used IBC Section 722 and, to a lesser extent, Resource A in the IEBC for determining the fire resistance of existing construction. This analysis is provided in a report that the design team can present to the AHJ to justify the construction type for the project.