The line <property name="useLocalJavadocUrl" value=""/> in define-solr-javadoc-url is obsolete, as this is not used here. It is only for Lucene to override some stuff (it disables SNAPSHOT mode and is Jenkins related). We may do the same for Solr, but this would require to move the "-SNAPSHOT" check to the groovy script and remove it from the XSL. My suggestion would be to use the same logic like for the Lucene Javadocs URL (same "if" statement) and if the URL is offline, leave it empty. The XSL would just do a check on empty solr-javadoc-url (if its empty) - and not the version - and then print the 2 variants (online or offline).
I can slightly modify the patch and upload a new one, ok?