The first question is does either car have active steering with ARS? Use only CHF11S in cars with active steering.
You may also try drawing a small sample out of the power steering reservoir with an eye dropper or straw (push straw in, cap end with your finger, draw straw out, hold straw over a clear container and release finger) and analyzing the color. CHF11S is a very light green.
I agree with your label deduction. If yours originally had a green label it is most likely using CHF11S. Most of what I see today in BMWs is CHF11S because it is a very stable fluid with a wide temperature range.
While mixing ATF and CHF is not recommended, I have read in BMW literature that if they are mixed together there is no reaction (no chemical changes, precipitate, etc.) but it is not recommended because CHF11S was originally recommended for arctic climates because it has a very low pour point (stays fluid at lower temperatures) and mixing ATF with it raises the pour point of the total mixture.
If you are still uncertain go to a dealer or indie and have them tell you what to use.