I received the below words from D365 support when inquiring about this issue. It is unreasonable to think that a user is going to manually set a cash discount on a vendor or vendors across 40+ legal entities in which that vendor works.

"CashDisc.PaidLedgerDimension field is mandatory but it is surrogate foreign key pointing to DimensionAttributeValueCombination.RecId. Data sharing works with natural key. If a field like PaidLedgerDimension is surrogate foreign key and mandatory, the field can not be shared. So the table can not be shared."