Seniority of direct recruited JE

Sir plz tell me how to decide seniority of direct recruited JE through RRB.

Plz clarify if a candidate sent for training to Training centre where training imparted in 03 different batches and at the end of training a retention test is taken out by parent organization, then what will be the basis of deciding seniority, either by  training school marks or marks obtained in retention test.