It is important to remember that NFPA 497 is a Recommended Practice. (Read the title) So is API RP 500. I value both of them highly and, as ANSI Standards, FedOSHA holds them both in high reqard as well; however, a locally adopted Code like the NEC trumps an RP in any court.

I am assuming from the Part you cited (5.5.6) you are referring to an to an outdated edition of NFPA 497. The 2017 edition is the latest and I will be referring to it later. Part 5.6.6 [2017] contains the same material you cited. You may find the last sentence of Part 5.5.4 of the edition you are using interesting as well - assuming you have the requisite "experience", of course.

Technically, the NFPA 497 Figures are only a recommendation. Of course you do have to “draw the line somewhere” and they represent the consensus judgement of history. However, you should also refer to NFPA 497 [2017 edition] Parts 5.8, 5.9, and 5.10. You will note none of the Parts mention “batches” as part of the underlying analysis.

As I said earlier, "I'm not there" so whatever you (and your insurer) are happy with is fine with me.