Under Article 21

I am a Army serving Junior Commissioned Officer and served the country for 27 years and 04 months. My retirement is due on 31 Mar 2015 for which my Record Office have issued Discharge Order. I was posted as a staff officer in United Mission in South Sudan (UNMISS) from 11 May 2014 to 10 May 2015 and returned back on 24 May 2015. After coming back to India I have applied for United Nations Job as a associate reporting and operations officer (UNMISS) and have been offered with the said post after clearing exam and interviews. I have applied for premature retirement stating same ground but was rejected citing an order issued during 1988 that once a person returns back from foreign mission will not get premature discharge for three years. The letter has not been prepared under any Army Order/Instructions nor any GOI ruling. The Letter states mentioning an example where a JCO who was part of training team and posted at Bostwana for period of three years and after returning back took premature discharge and joined the Bostwana Army "In view of the above you are requested to formulate a suitable policy and issue instructions to discourage the above practice. It is suggested that JCOs/NCOs/OR could be debarred from seeking premature retirement for a minium period of three to five years after completion of their deputation tenure abroad." For my case the situation is totally different as my retirement is due on 31 Mar 2016 and I am seeking employment in the worlds biggest security organisation. Can I file a legal case under article 21 and possible outcome.