Currently changes-to-html pulls release dates from JIRA, and so fails when JIRA is inaccessible (e.g. from behind a firewall).
SOLR-9711 advocates adding a build sysprop to ignore JIRA connection failures, but I'd rather make the operation always offline.
In an offline discussion, Hoss Man advocated moving Lucene's and Solr's doap.rdf files, which contain all of the release dates that the changes-to-html now pulls from JIRA, from the CMS Subversion repository (downloadable from the website at http://lucene.apache.org/core/doap.rdf and http://lucene.apache.org/solr/doap.rdf) to the Lucene/Solr git repository. If we did that, then the process could be entirely offline if release dates were taken from the local doap.rdf files instead of downloaded from JIRA.