It seems that the relationship between Stobart Air and the airports has become more "arms-length" than it was. I believe that EI own the -600s and lease them to STK, which probably dictates a large part of where they operate to. Stobart allowed flyBe to take over the DUB-SEN route, for reasons which were never clear to me. Its strange that they have never resumed the route - unless the aircraft can gain better returns elsewhere.
I think they part funded them however may as well own them as they are only for EIR ops. Now that was for the 6 ordered in 2013, since then they have almost doubled the ATR 600 a/c with number 11 been delivered in the last 2-3 weeks. 4 extra aircraft added to EIR within 12 months to take it from 10 to 14.