I am telling you the reason why overtakes often happens.
When 12802 departs ndls it catch 12418 till tdl.
Then from their onwards it trails 12418.
As it departs panki it takes line number 4 for Kanpur central.
Sometimes...
more... due to 2-3 consecutive trains between panki and cnb it trolls at outer
On the contrary when 12582 comes due to long queue at cnb outer on line 4 controllers give it line number 2 .
So due to it only sometimes it ot 12802 before cnb.