In the CryptoToken view it is possible to create multiple representations of the same PKCS#11 slot. Doing so makes no sense, since access to one's content would grant access to the others'. (It is however sometimes convenient for testing, so we can't prevent it entirely.)
The simplistic approach would be to warn when multiple creations of library+slot-identifier, but since the same slot could be referenced by id, index and label we should consult the list of mappings used to display slot labels.
Care must be taken to prevent failure on HSM that don't support label-matching.