Earlier 2841/42 & 6003/04 had 3/4 Dedicated rakes & without RSA system.
After becoming 12841/42 & 12603/04( later on 12839/40) -- RSA system was introduced around 2010. Coromandel & Chennai Mail must have own Dedicated LHB rakes. Also Coromandel must start from Howrah for better convenience to passengers & 12840 must have suitable arrival time at Howrah (21.45 hrs in place of 23.00 hrs). This is very necessary.