cancellation of his offer of appointment ab-initio

The petitioner applied for the post of steno and subsequently selected after fulfilling all codal formalities. The petitioner joined his duty but after 2 months he received cancellation of his offer of appointment ab-initio. Petitioner filed WP in the high court and court granted interim relief so petitioner again started his working in the concerned department. Petitioner served more than 16 months and received pay and allowances. Afterwards, the court decided and allowed the WP and declared impugned order as illegal and without lawful authority with direction to the respondent that provide the opportunity of hearing to the petitioner and decide the matter afresh through a speaking order. In compliance with the court decision, the department called the explanation of petitioner contending that his typing speed was 38wpm whereas requirement was 40wpm and department overlooked that point at the time of interview. So respondent called the explanation of petitioner that why his appointment may not be cancelled an-initio. In response thereto petitioner replied to the explanation that his typing speed is more than 60wpm. Petitioner also proved his stance through valid documentary evidence. But respondent treated the reply of petitioner unsatisfactory and declared that the offer of appointment was illegal so an illegal order can be withdrawn on the principle of locus poenitentiae. So respondent again cancelled the offer of appointment of petitioner ab-initio despite the fact that petitioner had served in such department more than 16 months.

So under these circumstances can an authority withdraw or cancel the offer of appointment of petitioner ab initio??
Please help in this regard.