I suspect one of them may have been 37612 as this is in a plain blue livery and is currently on hire to Colas. I caught it working 0Z38 1705 Crewe to Derby R.T.C and further digging on RTT shows a working in the opposite direction, with the same headcode, that left Derby at 1505, arriving into Crewe at 1629. Not sure what would have happened to the other loco, maybe it was dropped off at one of the depots around Crewe
Thanks for looking into, an interesting one!