Status codes for batch operations is always a mess. Do you return a 400 because one request made no sense even if the rest succeeded, or return a 200? 207 exists but it’s not really directly part of the HTTP spec and only seems to support XML response bodies.
Edit: @lysdexic if the RFC proposed a solution to responses for batch operations where some responses may contain errors, then that would be interesting. The RFC, from what I understand, proposes a format for error responses, but does not seem to support mixed error/success responses.