Castlefield Jn is no longer a mandatory timing point and thus trains aren't timed there. RTT only interpolates intermediate conditional timing points a day in advance.
The reason for this change is that the "closing up" signal, MP462, on the Up Oxford Road approaching Deansgate was removed as part of the Ordsall Chord resignalling, and so trains can no longer stand between Castlefield Jn and Deansgate.
That's aside from the fact that there were only ever 130 yards from the Junction to the end of Deansgate's platforms - so only an extremely short train such as a single Pacer could come from the Up Liverpool, and allow another train to proceed over Castlefield Jn towards Ordsall Lane/Water Street Jn whilst it sat at MP462.