Yes friend. Retention after two years of the post in case of Additional vacancy is mandatory. Without this formal procedure the service facilities like medical leaves, continuation, seniority, retirement benefits, gratuity, additional increments should get affected accordingly. One makes a simple mistake in case of additional post. Every one gives priority to the appointed teacher. But, in case of addnl. post the necessity of the post is of most importance. If the post itself does not get retained (It means the post was on a provisional basis, not permanent, to test whether the school can cope with the increasing number of students against the subject of the concerned post). And while a post is no longer required, it necessitates altogether a different procedure to abolish that post where the signature of the concerned teacher is needed to get transferred to a separate school. So, if your previous post was not retained and confirmed thereafter, you may have the followings to face-(i) Your previous post was not required but the required procedure was not done, (ii) You are not in a position to claim the service benefits. Please, discuss the matter with others. Don’t take the matter lightly. Even, General Transfer is not possible without retention of addnl. post.