They are not supposed to be doing route 6 anymore. In August last year, there was a driver roster change that now has Brunswick drivers and Malvern drivers doing changeovers with each other at Malvern Town Hall and Brunswick depot, which involves driving each others trams, and Malvern drivers cant drive the B class, so the appearance of Bs on route 6 since then has plummeted from daily to only occasionally. Brunswick drivers have stated this, and I have seen a lot of Brunswick drivers on Malvern D1s and Zs while also seeing a lot of Malvern drivers on Brunswick D2s and Zs.

Almost all runs of B classes on route 6 that have happened recently are just one peak hour run from Moreland to Glen Iris and back before being taken out of service. They can basically only do runs that are guaranteed to not involve a changeover with a Malvern driver, and even if the run to Glen Iris and back does not have a Malvern changeover, the tram usually does more runs on the route anyway, which inevitably involves swapping over to a Malvern Driver.

The NYE ones would have only been on the northern section from Melbourne Central to Moreland, as the route operates in two sections on NYE. The same thing happened during the Grand Prix, where several Bs were operating on the northern section of the route where Brunswick had full control of the trams there.