I think that your confusion is at first because of your premise as if only with reference to the particulars prescribed in the Form-C register you are going to compute the amount of bonus. It is actually not so because Form-C is the document only showing the net amount of bonus paid to the employees after deductions as per sec.17 and 18 of the PB Act,1965.
Second,because of your inadequate interpretation of the meaning of the phrase " working days". Literally, the phrase "working days" would mean with reference to the establishment the no. of the actual days the establishment was kept open for work and as regards the employees the no of days on which each employee was present for work. But, interpretation of the phrase for the purpose of bonus should be made only as per sec.14 of the Act which explains the computation of the no. of working days for the purpose of reduction in bonus mentioned in sec.13 of the Act. Sec.14 mandates the inclusion of certain days of absence in the no of working days which are (1) the days of lay-off (2) the days of paid leave (3) the days of absence due to temporary disablement caused by any employment accident and (4) maternity leave.
27th October 2017 From India, Salem