Versionable is an aspect, and CMIS does not support aspects, so it might be available in the <alf:aspects> section of what you receive. Do you use OpenCMIS or some other library to access CMIS? If you use OpenCMIS, see http://stackoverflow.com/questions/2998364
Well, I use another API and I use Alfresco extension to get the attached aspects, unfortunately this extension returns me only 2 aspects out of 5 attached. I reported that as a bug.