NACE and Frosio
There is some differences in material for stady.Nace pay more attention of Standards developed by NACE/SSPC/ASTM. FROSIO pay more attention on ISO standards. Some small differences in paint deffects terms. In NACE You can find more info about linings - rubber for example etc. In Frosio You can find more for marine coatings. Of coarse NACE provide various coarses as Marine, nuklear etc but that is separate coarses with additional money to pay. Differences in examination form. NACE has 3 levels. 1 and 2 are test. Level 3 is speaking - peer review. Frosio examination is by writing. Differences are not too much so if You has some certification is easy to pass examination of other organisaqtion. Same happened with me. I had Frosio certificate and later I had not any problems with NACE examination. It is matter of wish, time and money of coarse. USA companies are more interested with NACE certificate holders. European companies - FROSIO or Icorr.
I hope this short info is helpful for you.