Esi on arrear - employee whose salary was 400 per day increased to 600 per day

1. An employee whose salary was 400 per day increased to 600 per day. It was declared on November 2017and increase was to be paid from may2017 onwards.whether we have to remit ESI contribution on increase of Rs.200 per day from may onwards
2.An employees wages was fixed on November 2017. He was working from may 2017to November without salary. now Whether we have to pay ESI on his salary for the period may to nov.

It is clarified by ESI in their booklet as follows:
FREQUENTLY ASKED QUESTIONS ON ESI SCHEME
(This booklet is only for awareness purpose and can’t be referred/ quoted as legal )
16. What is the effect of increase in wages from a retrospective date?
In case the wages of an employee is increased from a retrospective date resulting in crossing the wage limit prescribed, its effect on coverage of that employee is only after expiry of the Contribution period during the currency of which such increase is announced or declared. The contribution on enhanced wages is also payable from the month in which such increase is announced. There is no need to pay the contribution on the arrears for the period prior to the month of declaration/ announcement/ agreement.