Once the rest of the batch of 25 new ADL E300s enter service at Stockton there will still be approximately 12-15 non-DDA MAN ALX300s remaining which, along with the non-DDA active reserves, have to be replaced by 1st January 2016.
The predictions for next years orders at the moment may either be Stockton receiving more investment, or another depot receiving more investment with the displaced vehicles being cascaded to Stockton. "mrnut85" did mention that there was a "little" rumour going around relating to the replacement of 22050/67/70 and the possibility of vehicles being cascaded to Stockton, but I think its best to wait until the beginning of next year when the 2015/2016 order is revealed.
Moreover, when the north east order press release was issued at the beginning of the year, it mentioned a total of 51 new vehicles for the north east which consisted of Gas Buses 28018-40, ADL E200s 37143/4, ADL E300s 27157-81, and one mystery vehicle. Was this a typo error or is there another vehicle expected to be delivered?
When Robin said "27's" I think he was referring to the fleet numbers of the new vehicles (27157-27181) rather than the number of vehicles being delivered.