Had it happen to me with a bubble coral. I bought a some xenia on a skeleton(rubble). After I but it in quarantine I saw some fluorescence under the actinics. I moved the xenia off and there was something small. Once in the DT it was big enough to ID . That was three months ago. Sometime there can be more then on colony (at least with the bubble and some disc corals) that comes back. If never tried to frag one though, then again I don't have a bandsaw.