I don't know who your source is but according to the GNE wesbite the 61 is still branded as drifter and it's new timetable is drifter green. Also it makes no sense what's so ever to change a brand completely when it still a well-known name. There is also the simplicity weekly ticket and to have a service branded as Simplicty but unable to use it on that service is very misleading for passengers. The Simplicty brand has no connection to the route of the 61.
Everyone is intitled to their own opinions, however, I find it hard to believe brand new buses could be ordered for a route that isn't considered one of the main routes. The 39 isn't exactly one of GNE's most profitable routes, hence why they don't even run it on evenings, like the 60 is. The original information stated that Drifter & Saltwell Park were to get StreetLites, and I find it hard to believe they totally changed that it seems a bit unorganised for a company like GNE. My personal theory, feel free to disute, is that 5 drifter Versa will go to 61 with the other three along with the spare simplicity Versa may move onto the 39.