grammar cache and xs:redefine

Suppose you have a schema A and schemas B1 and B2 which
redefine element E from schema A (differently).  They all have the
same namespace (call it alpha). Suppose your application maintains
a grammar cache with these schemas

Since the namespace no longer uniquely identifies the schema, how
does one decide which schema to use from the grammar cache
when a  document contains schemaLocation="alpha some-url" - or
does one use the url to disambiguate ?  Since B1 and B2 are different,
it is not clear which one should supercede A.

Or is it just a bad idea to have multiple grammars with the same
namespace and avoid xs:redefine.