Whoops, my bad. All this time I thought those were from 2004 lmao, just did my googles and the oldest batch of orange sign MCI's in MTA Bus is from 05, not 04. I always thought the 4300s came in around when that first batch of MTA Bus MCI's started coming in.
With that being said, it would make more sense for them to go to MTA Bus to retire buses older than 07, unless the 4300s are in really bad shape, IDK what kinda shape their in.