I was surprised while reading the discussion related to subpart V that nonmelting clothing is considered good to 2 cal. It kind of makes sense since 1.2 cal on the Stoll curve is for bare skin. Anyone else ever heard of this? I've heard it once in a while but not sure what the science is behind it, if any.

It was news to me when I read the new OSHA doc. It is also in 1910.269 in addition to 1926 Subpart V.. In the preamble there is a footnote that reads:
NFPA 70E-2012 no longer explicitly permits "nonmelting flammable materials" for exposures from 1.2 to 2.0 cal/cm2; however, NFPA 70E-2012 Table 130.7(C)(15)(b) apparently permits such fabrics for certain exposures above 1.2 cal/cm2. Consequently, the latest edition of NFPA 70E does not conflict with OSHA's decision to require flame resistant clothing for extimated incident heat energy exposures exceeding 2.0 cal/cm2

Perhaps they were attempting consistency with NESC, which does not require arc rated clothing below 2.0 cal/cm^2 IE. I'm unaware of the science behind it, though.

Currently (2012) NESC reads:

NESC 410A.3 "If the assessment determines a potential employee exposure greater than 2 cal/cm2 exists (see Neal, Bingham, and Doughty [B63]), the employer shall..." do a detailed analysis or use the tables in NESC and then wear appropriate PPE.

The tables in section 410 only support a 4 cal or higher clothing system. There is no mention of 1.2 cal/cm^2 or 2 cal/cm^2 anywhere in the tables.

So I can understand the desire to reconcile the range of 1.2 to 2.0 cal/cm^2 (and that's the question I'm asking!) but I'm not seeing support for it. I know that during the last NESC Code cycle there was strong discussion about dropping this standard down to 1.2 cal to match other standards.

I am sure it provides some level of protection, but I wouldn't think you could just assume it is 2 cal/cm2. In order for it to be "officially" 2 cal/cm2 it would have to be labeled as such.