NEC and IEC 60346 equivalent


Good evening folks !

Im currently reviewing a Project made by Spanish contractors in Mexico (funny isn't it ?),

These guys used the IEC 60346-5 for their wiring calculations instead of the Mexican nom (The mexican nom is a copy of NEC 2011 so ill just refer as NEC now),
We are trying to see if they do match,
As far as I can see temperature derrating is the same on both normatives, yet when you get to 60346 table B52.20 for grouping it gets interesting, link to that table below

Correct me if im wrong but what we use for grouping is 310.15 (b)(3)(a), and its totally different for the table used in this project per IEC, and I do not recall something similar in the NEC.

Have any of you guys come across projects like these where IEC is used instead of NEC?
Any recommendations