(1) If a municipality enters into a coverage agreement under this Article prior to having established a pension plan under Article 3 or 4 of this Code, all police positions and all firemen positions, including members of a volunteer fire department organized pursuant to municipal ordinance, shall become subject to social security and be included within the absolute coverage group of the municipality in compliance with Section 218(b)(5) of the Social Security Act. If a municipality establishes a pension plan under Article 3 or 4 of this Code subsequent to establishing social security coverage under the conditions set forth in this subsection, the police and firemen positions shall remain subject to social security as part of the original absolute coverage group.
     (2) If a municipality enters into a coverage agreement under this Article subsequent to having established a pension plan under Article 3, 4, 5 or 6 of this Code, or subsequent to becoming legally obligated to establish such plan even though having not complied, all police and firemen positions included under such pension plan shall be exempted from social security coverage and excluded from the absolute coverage group of that municipality pursuant to Section 218(d)(5)(A) of the Social Security Act.
     (3) If the covered or non-covered social security status of the police and firemen positions in a municipality has been determined under the conditions set forth in either subsection (1) or (2) of this Section, such covered or non-covered status shall remain in effect in the event the municipality shall begin participation in the Illinois Municipal Retirement Fund pursuant to Sections 7-132 and 7-134 of this Code.
     (4) Police and firemen positions which have not acquired social security coverage as part of an absolute coverage group under an agreement executed by the municipality pursuant to Section 21-103 shall not acquire social security coverage by virtue of the municipality’s mandate to participate in the Illinois Municipal Retirement Fund under Section 7-132, or the municipality’s election to participate under Section 7-134.
     (5) Incumbents occupying police and firemen positions who because of age, physical condition, length of service or other disqualifications are ineligible to participate in local pension plans established under Articles 3 and 4 of this Code are also excluded from social security coverage if the employing municipality has obtained social security coverage under the conditions stated in subsections (2) and (4) of this Section, except that beginning July 1, 1991, such persons are subject to mandatory Social Security coverage.