Each employee subject to this subtitle is required to complete a 6-month probationary period as the final step in: the employee's initial appointment to a position in the State Personnel Management System; the employee's appointment to a position in the skilled or professional service following a competitive promotion; and except as provided in subsection (b) of this section, the employee’s appointment to a position in the skilled or professional service following a reinstatement. An employee is not required to serve a probationary period if the employee is reinstated within 1 year after the employee’s separation from State service to a classification in which the employee had previously completed a probationary period. To successfully complete a probationary period, an employee is required to demonstrate proficiency in the assigned duties and responsibilities of the position to which the employee is appointed.