With the setup on SOLR-10006, after removing some index files and starting that Solr instance I tried issuing a REQUESTRECOVERY command and it came back as a success even though nothing actually happened. When the core is accessed, a core init exception is returned by subsequent calls to getCore(). There is no catch block after the try so no error is returned.
Looking through the code I see several other commands that have a similar pattern:
and perhaps others. getCore() can throw an exception, about the only explicit one it does throw is if the core has an initialization error.