It's somewhat common practice to continuously upgrade the routes that make the most money and/or have the most potential to grow, its not unique to just GNE in the NE, Arriva's favoured routes for new stock is the X21/X22 at Ashington and the 1/5/5A & 7 in Darlington whilst Stagecoach upgrade the 36/37/38 on Teesside roughly every 5 years, this in turn allows cascades to some other busy routes and then again to lower used routes a bit further down the line.

In four years from now you have to think that if little/no other investments are made, the 27 will have 14 year old B9s and Tens will be 12/13 year old, whilst brand new buses would be nice for these routes, 5 year old StreetDecks and E400s are still an upgrade over what is currently used.

Consett/Stanley has been somewhat the forgotten middle child up until recently, about the only real big investments was the 45/46 and even that went 9 years between the Omnis to the Lites and the Ventures in 2013, beyond that the likes of the 15/15A & X70/X71 felt like the place where deckers go to die, of course 16/16A got new Lites in 2016 too but now being replaced with older B5s but an upgrade in capacity, 2015 was the point things made a slight improvement with some new stock and slightly younger cascades, the ex London B9s was a good start in terms of improving things but I think there's been some potential for more.