Dear Christoph,
once again thanks for this very detailed answer. I classified it as "helpful" as I fear there is no final "correct anser" to this issue.
To summarize: usage of REAL_SUB_E is depending on the amount and quality of data you want to store for each supplier, given the fact that there are at least two suppliers for the same RAW material (which means the same chemistry).
In case it is sufficient to store only the suppliers SDS this can be done by using different instances on REAL_SUB level.
I hope I got your message right (I know that this is a very simplified summary).
Best regards,
Christoph