Have a recent experience (after Status Match from BMI to BA).
I am Sapphire and my wife is Emerald
1. DME-BOJ in Z class (cheapest economy) - myself being upgraded. I sent wife with infant to my upgraded seat.
2. VAR-DME. I get upgrade, but it was only nice seat. Meal was standard economy for all pax. I asked FA, and she told that this flight is single class flight.
So, for me two upgrades in four flights, not bad.
my wife will fly in a week with two kids back from BOJ. I will post details.