“year of assessment” means any year or other period in respect of which any tax or duty leviable under this Act is chargeable, and any reference in this Act to any year of assessment ending the last or the twenty-eighth or the twenty-ninth day of February shall, unless the context otherwise indicates, in the case of a company or a portfolio of a collective investment scheme in securities be construed as a reference to any financial year of that company or portfolio ending during the calendar year in question.