No, the 6 trains DO NOT crossover from normal off-peak train
duties. Direct comes from Bishan Depot itself. As to how does
Bishan Depot gains back 6 trains, they are gradually added back
into Bishan Depot when Ulu Pandan sends down trains during evening
peak.
Anyway, the 6 trains during morning peak are in this format:
040
041
042
043
044
045
Using last year's timetable 040 041 042 043 all head back to Changi
after morning peak while 044 and 045 continues full day until pm
peak.
Anyway the shuffling of trains between the 3 depots is a bit very
confusing but I'm very affirmative the number of trains in each
depot return to original number after each day.