This slip gets attached to 17225 on Tue, Fri and Sun (3 days per week) at GTL (and goes upto UBL), and gets attached to 18047 on Mon, Wed, Thu and Sat (4 days a week) at GTL (and goes upto VSG), which is
/train/22284 and called as slip no II.
So the departure days for this train (from KCG to UBL) should be Mon, Thu and Sat at KCG. So, your logic is correct, but info is wrong.