Small UNIQUENESS ambiguity

RFC 3159 section 7.9 says:

   If a PRC and its sparsely augmenting PRC both have UNIQUENESS
   clauses, then the UNIQUENESS constraint for instances of each PRC
   MUST be applied according to the UNIQUENESS clause in the
   corresponding PRC definition.  Note that a sparsely augmenting PRC
   thus can override the UNIQUENESS clause of the PRC it sparsely
   augments.

However, it does not specifically state what the rules are with regards to
using UNIQUENESS clauses with non-sparse augmentations (AUGMENTS rather
than EXTENDS).  I am inclined to believe it is not permitted, given the
one-to-one correspondance between rows of one PRC and those that augment
it.  But as it's not specifically forbidden, I thought I should seek
clarification before I consider something an error that isn't.

Thanks.

--
Michael Kirkham
www.muonics.com