Not sure if this has already been mentioned but dates for GWR 150 cascade to Northern are:
Sat 3 Feb 150101, 150104, 150106, 150108, 150123, 150128 & 150129
Sat 17 Feb 150120
Sat 3 Mar 150121
Sat 17 Mar 150127
Sat 31 Mar 150130
Sat 14 Apr 150131
If this is the wrong thread for this please...