Fetch request blocks are only used on successful mappings, if the 401 raises an error then nothing should be deleted - if you don't have a mapping for it.
RKStatusCodeIndexSetForClass(RKStatusCodeClassClientError)
covers all of the codes in the 4xx range. You don't need to use that. If you want to ignore the 401
response from the mapping then you can create an index set containing only 400
(or 400
, 402
, etc as required).