As per case facts, appellants, who originally belonged to the Railway Board Secretariat Service (RBSS), were promoted to the Indian Railway Personnel Service (IRPS). They were granted seniority with a ... five-year weightage for past service, as per Principle (7)(a) for determining the relative seniority of Class 1 Officers. Respondent No. 1, a direct recruit for IRPS, challenged this, arguing that he should be senior based on his earlier appointment as a direct recruit. The Central Administrative Tribunal sided with the respondent, holding that the appellants could not be ranked senior to him. The question arose whether seniority should be determined solely by the date of appointment or if principles granting weightage for past service to promotee officers are valid and non-discriminatory. Finally, the Supreme Court ruled that the principle of granting seniority based on weightage for past and lower service to promotee officers is well-known and recognized in service jurisprudence. It is not an invariable rule that seniority must be determined solely by the date of appointment, and any departure from this rule, especially when the relevant principle was not challenged, was found not to be unreasonable or illegal.