A number of the Solo's at Durham haven't been used in quite a while (since the temporary PVR reductions on the 6/64). At this point Solo's aren't really suitable for any of Belmont's services, so if they went there to replace them, coinciding with those PVR's re-increasing, that would make sense. I imagine Arriva will be due more cascades to replace the remaining Omnicities, B7 Gemini's and the similar excess of Solo's at Jesmond over the course of this year.