My father joined Navodaya Vidyalaya in 1992, after serving the Arunachal Pradesh government’s education department for 19 years. His pay scale back then was 2200-75-2800-EB-100-4000, which I found on his PPO. However, the pro-rata pension they calculated is significantly lower than expected.

Based on the information provided, your father’s pension should be calculated based on the pay scale in effect at the time of his retirement and not just the initial pay scale. You may need to consult with a pension expert or legal professional to ensure the correct calculation of his pro-rata pension. It is possible there are discrepancies in the calculations or a misunderstanding of the applicable pension rules.