TransformationEquationInstruction can cause "corollary" facts to be added to the module based on existing facts. If some of the base object ids associated with existing facts are gone from the module then construction of corollary facts can fail. We either need to be more conservative about whether to add corollary facts, or be more conservative about when to assert that data descriptors are well-formed, omitting such checks in cases where the object associated with one or other data descriptor is no longer present.