Thanks for the data point; sorry (but not really very surprised) to hear that it didn't work. What you now need to do is add up the BD and other flights you've got lined up between now and the end of the summer and decide whether NZ, BA or another airline is going to be your preferred partner going forward.

If you have sufficient BD + *A flights to get Diamond Club status then that might be worth doing -- and would definitely be worth doing IMO if you'll hit Gold, as BD Gold is easier to achieve than BA Gold. Alternatively, you might be better off crediting those BD flights to BA if other BA and OW flights make that your faster route up the BAEC status ladder.