And also do not replace one by the other.
Some people from the German 7-Forum and also now from the E34 Forum in German had contacted Pentosin. One got the reply by email, the other one talked with a head of a labority there.

To make the story short:

1. Where Pentosin CHF 7.1 is mentioned on the sticker of the reservoir, only refill CHF 7.1.

2. A mixing with other hydraulic oils could cause that additives could separat as a flocculent , which then could block valves etc. The instruction not to mix it is mentioned on the cans of the Pentosin 7.1
That is apparently also mentioned in a special internal BMW info for the repair shops.

3. CHF 7.1 contains special lubricants/additives, which are required by the older systems on E32 and E34
CHF 11S does not contain these additives in the required volume, it therefore cannot be used as alternative or replacement for 7.1 in case of topping up and/or replacement of Pentosin 7.1.

4 CHF 7.1 is green; CHF 11 is also green, but the colour is a slightly lighter green.

Here a copy of the email received in Germany from Pentosin:

Guten Tag Herr xxxxxxx,

vielen Dank für Ihre Anfrage, beide von Ihnen genannten Hydrauliköle CHF 7.1 und CHF 11 S dürfen nicht vermischt werden, da es zu Unverträglichkeiten von Einsatzkomponenten bei Vermischungen kommen kann, was wiederum im schlimmsten Fall zu Ausfall des Hydrauliksystems führen kann.
Dies gilt für Nachfüllungen, wie für Neufüllungen.

Wir hoffen Ihnen hiermit weitergeholfen zu haben und verbleiben

Mit freundlichen Grüßen
Deutsche Pentosin-Werke GmbH.