This summer (2013) those routes from Derry are operated by Thomson on a W pattern with the Belfast based aircraft. Next year, the Belfast based Thomson aircraft has no W patterns (ultimately meaning two extra flights a week from Belfast).
It will be interesting to see what Derry gets instead if it doesn't turn out to be Air Europa as with AEA0000 as flight numners, it doesn't look that definite yet!
It's also interesting to note that Northern Ireland as a whole has a greater choice next summer thanks to the Derry services not being served by a Belfast aircraft.