Northern only own one Beech 200. The other is operated on their AOC. The 421 no longer belongs to them, so perhaps the Citation if it does exist will possibly only be on Northern's AOC.
I see a couple of Northern's Ce 152s have gone somewhere along with the Pa28. Parked somewhere cheap?
As for mail flights, last time the tarmac was replaced at NCL the post office drivers loved it as they didn't have to drive so far from the main sorting office. Isn't it in Darlington or Bishop Auckland??
No sign of Parmo's prophecy either.
Off to watch Boro thrash Man U on TV!