I had working combo on nüvi 2460 of CNEU2012.40 with FULL_CXEU2012.40, both of them worked fine. I have updated CNEU2012.40 to CNEU2013.10 and I see no more the FULL_CXEU2012.40 in the list of the maps.
If I delete the CNEU2013.10 img, the FULL_CXEU2012.40 works fine. (No other CNEU maps installed.)
If I copy back the CNEU2012.40 img, the FULL_CXEU2012.40 works fine.
It is only if the CNEU is newer the older CX is not visible.
(It was the same in the 2012.30->2012.40 update as far as I remember.)
I'm waiting for the new CX EU 2013.10 unless you have other ideas, what to check or how to solve.