6118-6121 were dealer stock vehicles, and looking at their chassis numbers on bus lists on the web, they were built around Feb 2014 as part of a large batch of unregistered 40-50 Volvo B9TL / Wright Eclipse Gemini 2s as dealer stock before engine emission rules came into force. The dealer stock ended up with GNE, EYMS, Arriva North East, Preston Bus, Bus Vannin (IoM) plus various independents.

Whilst 6334-6337 were built as follows....
6334 / 6335 - Early 2014.
6336 / 6337 - Mid 2014.

The registration of a bus doesn't always reflect the true age of the vehicle. Sometimes vehicles are stored somewhere in a shed or field. Hence why Bob Smith Travel had 3 Plaxton bodied coaches build in the 1970s on E Prefix Plates (E901DRG/E902DRG being Bedfords and E903DRG being a Ford). There is a number of other examples like a number of LHD Leyland Atlantean products failing to reach their intended destination abroad and recieving a later registration, this includes a D registered Willowbrook example with Go Whippet and a F registered Neoplan bodied example running as a Non-PSV.

In fact two vehicles new to GNE have registrations suggesting they are newer than the rest of the batch, that being Omnicity 5268 (07 instead of 56) and B9TL 6083 (13 instead of 62) which were both damaged on delivery and were delayed due to repairs that by the time they arrived they qualified for a newer plate. And of course the latest delivery of Streetdecks, some of them are a good few months to possibly a year older than the rest of the same order due to issues with Wright Bus seeing some of the earlier examples being sat stored in Northern Ireland.