So what you are saying is when GM or ZF design a transmission for BMW they are also designing a fluid that has NEVER be produced by any fluid manufacturer EVER before? I find this extremely hard to believe. I am willing to bet my transmission that BMW is given an existing fluid spec by the trans manufacturer, contracts a fluid provider to produce the fluid to that existing spec, then puts a BMW specific part number on that product so it can be entered into their production parts ordering process and parts inventory system.
I did a triple dump and fill (90% new fluid) with the Bentley cross ref specified Esso LT 71141 (Castrol inport car formula, Meets LT 71141) on my "03 X5 4.4 at 100k miles, have put an additional 50k miles on the truck (over 2k miles with a combined trunck and trailer weight of over 12k lbs) and have seen no issues. At least in my instance, the Bentley cross ref fluid was right on the mark.