While I don't know the reg, I was pleased to experience the upgraded cabin on the A333 PHL-MAN in Y and MAN-PHL in Envoy last month. I was very happy with the new Envoy and find it better than the UA C class.
I was following this quite closely in another forum before my vacation in the US last month and at that point only N270AY and N271AY were left to be upgraded. But I think this may be out of date by now.
I was on 273 twice last month also on MAN-PHL, PHL-MAN and the Y experience was the best I have had with any US airline.
I believe the last one or two are in for upgrades, leaving no remaining A333s with the old cabin.
Flew N276AY on PHL-MUC last week in Envoy. It's the same product as on the A330-200 fleet, and very nice. It's nice to see US have a real international business product at last. I haven't been in Y yet on the updated A333.