Written Agreement Required for Transfer of Leave Credits. For the purposes of applying the provisions of this Article, employment in the Executive or Legislative Branches of State service shall be credited as service in the Unified Court System; provided, however, that except as otherwise provided by law, leave credits may not be transferred upon movement from such positions to positions within the negotiating unit except where such credits are earned and accumulated in accordance with attendance and leave provisions which are substantially equivalent to the time and leave provisions of this Agreement and there is a written agreement between the President of the Civil Service Commission and the Chief Administrative Judge governing the transfer of leave credits upon such movements. Other public employment may be credited as service in the Unified Court System for purposes of determining transferability of leave credits provided such employment was subject to attendance and leave provisions substantially equivalent to the time and leave provisions of this Agreement, and provided there is a written agreement between the Chief Administrative Judge and the public agency wherein such employment occurred governing the crediting of such employment and the transfer of leave credits upon movement of employees to and from such agency and positions included within this negotiating unit.