28.1(1)Regulations made under paragraphs 28(a) and (a.1) may be retroactive in their operation to any date before or after the commencement of this subsection specified in the regulations.

28.1(1.1)Regulations made under paragraphs 28(g.1) to (g.5) may be retroactive in their operation to January 1, 1997, or to any date after January 1, 1997.

28.1(1.2)Regulations made under paragraph 28(h) may be made retroactive.

28.1(2)Regulations made under paragraph 28(h.1) may be retroactive in their operation to November 30, 1994 or to any date after November 30, 1994.