This Act shall apply in relation to any renewal of authority made before 30th September 1984 as if the provisions of this Act which derive from provisions amended by section 16(a) to (d) of the Mental Health (Amendment) (Scotland) Act 1983 and any amendments in Schedule 2 to that Act which are consequential on that section were included in this Act in the form which the provisions from which they derive would take if those amendments were disregarded; and, where an authority has been renewed before that date for a period of 2 years of which less than 16 months has expired on that date, that period shall expire at the end of 18 months from the date on which it began.