I checked-in 58KG on 252 last week as a DM Y (non-student tix) pax without paying any surcharges.

When she had added up the weights of my bags,she requested to have a look of my hand carry,which was a small laptop bag. I guess the reason I was not charged is because she put my 15KG hand carry allowance to my 40KG check-in allowance plus +/- 5KG.