Those might be the long Enviro 200 MMC's as well, the better version with the 6 cylinder 6.7l engine. I have observed that ADL tend to register the 6 cylinder ones with the YY reg and the smaller ones with YX.
Go North East needs to invest in something like these permanently though. There is always Solos on full size routes at Washington like the 8 or 50
RE: Go North East - State of the Fleet