Maybe 1248, 1272 & 1277 are in storage? But then again giving how demanding the BX artic routes are in terms of buses needed, I don' t think they can afford to put buses to storage for the summer. Things could be interesting if those three buses don't reappear after Labor Day weekend.
Only other thing I could think of is they need parts or are getting heavy duty work at an CMF. Can't see them starting to retire the 1200s with no new artic order for the foreseeable future. Also I thought the Nova artic is a durable bus, I would be surprised to see the TA starting to write them off at only the 12 year mark.