Please correct me if I'm wrong.... But it sounds like they're confused
My understanding of that is that they claim their testing standard = 28.4" head excursion only (untethered is not allowed) & that US = 32" only. They're wrong. US = 32" untethered / 28" tethered. So, while they claim CMVSS is "better" reading further it seems that FMVSS is "better" by .4"
I don't believe one is truly better than the other -- US should require top tethering like Canada does, but Canada should allow for higher weight harnessing. Especially for seats that are designed exactly the same save for different stickers & manuals to suit the different regulations!
So, this has not changed my mind: I'd still risk a ticket rather than put an obese toddler in a
booster before the maturity level is acceptable for proper use *SHRUG*