1861 HWH-BWN Service was 1 & 2 Mail (Evening DEP)
29 Dec 1866 Departing HWH-Delhi Mail arrived Delhi with 17 Coach (Full Construct with Evening DEP)
1867: HWH-Delhi Service was 1 Chord (Evening DEP)
1868: MAS-Beypore Passenger split to MAS-SBC Passenger at JTJ, 3 Class attached at SA (Morning Dep)
1913:...
more... MAS-MAQ through Coach detach from 10 MAS-MTP Mail and attach to 16 Mail at Podanur (Evening Dep). MAS Morning DEP Passenger is now MAS-MTP Pass
1935: 10 Mail named Nilgiri. MAS-MAQ New Service as Malabar Exp
1955: Malabar Exp Named as Mangalore Exp
1960: Mangalore Exp become 1 MAS-MAQ Mail
So stop highlighting Through Coach Attach/Detach any issue for a train which was Mail since 1861.