(a) No affected district shall be again involved in proceedings under this Article for at least 2 years after a final non-procedural determination of the first proceeding, unless during that 2-year period a petition filed is substantially different than any other previously filed petition during the previous 2 years or if an affected district is identified as a priority district under Section 2-3.25d-5 of this Code, is placed on the financial watch list by the State Board of Education, or is certified as being in financial difficulty during that 2-year period.
     (b) Nothing contained in this Section shall be deemed to limit or restrict the ability of an elementary district to join an optional elementary unit district in accordance with the terms and provisions of subsection (d) of Section 11E-30 of this Code.