MAG has a dedicated route development team for Manchester Airport, based in MAN. A number of them are in World Routes in Istanbul this week.
Most airports which are part of a group are listed as part of the group or under one of the attending airports, which is a direct function of the increasingly rapacious charges that the event organisers expect airport participants to pay.
Does it matter? No. The majority of meetings taking place at Routes are requested by the airport attendees of the airlines. Very few - probably less than 10% - are where an airline wants to meet with an airport. So if you're part of ABC Airports and you're Airport B, you still request to see the airlines you have on your target list even if those might be different from those which your sister airports A and C wish to meet. It's pretty much irrelevant given the format of the event.