@j636
With the new terminal and gates layout, it's important to not think of gates as being necessarily associated with either of the terminals. Yes, the 400 gates (formerly Pier E) are physically part of the T2 development, in the same way as the 300 gates (formerly Pier B) are part of the T1 (formerly the Main Terminal) development.
But now, the Terminals are the check in/departures and arrivals areas and all the gates are accessible to either Terminal via an air side connection. So a passenger checking in through T2 could depart via any gate, similarly an arriving flight could disembark passengers at any gate and have them "arrive" into either terminal (in practice, T2 pax will mostly depart and arrive via the 400's).
JAS.
BTW, There was an interesting little historical snippet on the radio a few days back. A DAA spokesman was discussing the bus drop off/pickup and car park arrangement and mentioned that T2 is the 5th passenger terminal to be build at Dublin. 1st was the Central Terminal (now known as the "Old Terminal"), then there was a temporary structure known as the "Lourdes Terminal", the North Terminal which is beside the Old Terminal, followed by the Main Terminal (now T1) and now T2.