This discussion clarifies seniority between two candidates, X and Y, based on their Engineering Service Examination (ESE) selections. Candidate X was on the reserve list for ESE-2011 and joined in May 2015, while candidate Y was on the main list for ESE-2012 and joined in April 2014. Seniority is determined by the examination year and merit rank, not by being on a reserve or main list within the same year. Therefore, someone selected in an earlier examination year is senior, regardless of their initial list placement.