My initial response is, “Don’t worry about it; it isn’t a Class III installation.”
If an installation isn’t within the scope of Articles 511 to 516, attempting to classify from Article 500 is a good example of “This Code is not intended as a design specification or an instruction manual for untrained persons.” [Section 90.1(A)]
In over 45 years, I’ve never run into a “trained” building official with respect to classifying a location although many are quite competent with respect to the installation itself. Building officials are prone to over-classifying “just to be safe.” I’ve met a few competent insurance AHJs
Section 500.4(B) Informational Notes lists several external references that should be used to classify a location. Unfortunately, none of them deal directly with Class III. NFPA 499 now deals more or less with classifying both Class II and III.
Several Article 503 exceptions hint at the housekeeping concept Golddigger referred to; e.g., Section 503.125. Although it is more a protection technique than modifying the electrical area classification.
Until Article 506 included Zone concepts, Class II and III were pretty much separated. If you read Article 503 carefully, you will find Class III is more interested in flash fires than explosions. You will also find there is virtually no difference between Division 1 and 2 installations.