27. Date at which workers to be counted---Where, in any year, it is
 necessary, for the purposes of any provision of sections 24 to 26 of
 this Act, to count the number of workers employed by an employer, those
 workers shall be counted as at---
   (a) Such date in that year as the Commissioner shall, for the purposes
         of this section, specify from time to time, by notice in the
         Gazette, in relation to that employer or in relation to any
         class of employers to which that employer belongs; or
   (b) If no date is, for the purposes of this section, for the time
         being specified by the Commissioner in relation to that employer
         or any class of employers to which that employer belongs, the
         31st day of January in that year.