DDSXTY14 — Discriminator default semantics are unclear

The spec says "any discriminator value that does not explicitly identify another member is considered to identify the default member". This sounds like "if a given discriminator value does not appear in a union case definition, then that discriminator value identifies the default member". (As a side effect, this means that unions with a default case can never have cases added or removed, even if marked as appendable or mutable, since a receiver would have to interpret the discriminators of unknown cases as indicating the default member. I am unsure if this is intended, but a non-normative note should possibly be included.)

However, then it says "it is not required for every potential discriminator value to be associated with a member", which seems to contradict the previous claim.