Having read and heard a lot of how "even the Apex Court has let Veterans down", please bear with me for a contrarian point of view.
One Rank One Pension was possible till 1986 because the Armed Forces Pension Revision Committee (AFPRC) laid down in 1949-51 that every rank will get a pension which will be a fixed amount sunject to the different minimum service but full pension would be paid when one completes 33 years of service.
The pension was Standard Rate of Pension (SRP) and it was independent of the residual service i.e. number of years one spent in the rank that one retired in as well as the pay earned on date of retirement/death. In other words, it didn't matter if the pay was minimum of scale at Rs 1500 or maximum of scale of Rs 1700, the pension would be Rs 550.
However, subsequent to the Parliament approving Pay & Pension Rules for judges of the High Courts and Supreme Court wherein pension was determined to be 50% of the average pay last drawn over a period 36 months, 4th CPC recommended and Govt approved the same principle for Armed Forces personnel.
The consequence was that those promoted to a rank earlier than their course-mates or senior who were bypassed earned more than their course-mates or the ibid seniors. As every year of service meant an increment to the salary/pay, the pay of those who served longer in a rank (residual service) earned higher amount as pay than their course-mates or seniors who were promoted later.
That formulation effectively destroyed the SRP and the same rank, same pension principle! As for same years of service on date of retirement/death, it all depended on residual service in the rank. Different periods of residual service, different amounts of pension for the same rank and same number of years of total service.
As for Courts not interfering with policy decisions, there is a principle/doctrine of Stare Decis i.e. courts will not give a different interpretation if there exists an interpretation in another judgement. This article may be of interest
'Policy decisions not to be disturbed unless found arbitrary etc
