There are a lot of G7 "certified" printers in the US but most of them only know what they remember from their class and have very little experience. That is the croud your dealing with. The official ISO color standards are the CRPC profiles available on color.org. So if your printer does not know what profile they are using or which color space they print in, you can figure out what solor space they "Should be" printing in by knowing their print process. Sheetfed Offset, Wide Gamut Digital, Web Offset, white paper, or Web Offset yellowish paper, or Uncoated, or Newsprint. That print process information can allow you ( or anyone else) to figure out what the printer is supposed to do.
G7 is another Pillar, different but very similar to the printing process for Fogra coated for example. The difference is very slight in the highlight areas, if your being picky. In reality what qualifies for Fogra coated will print very closely to G7 coated CRPC6. The Advantages of G7 over the european standards is it's paper relative. Now an argument can be made for color standards that include papers, but todays papers mostly change via optical brightners, so that is not a simple calculation.
Not quite sure what you mean by "overwridden". once a file is in a CMYK colorspace / profile is is only correct for that specific colorspace. So make sure your file workflow includes the correct US profile and embed it in the files.
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