Year End Discretionary Matching Contribution amended to x% payroll by payroll Matching contribution

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Year End Discretionary Matching Contribution amended to x% payroll by payroll Matching contribution effective June 1.

Client made the 1st payroll by payroll matching contribution in June for the payroll period ended March instead of the effective date of June.

Is this permissible to back date (effective date was June 1st for payroll by payroll) and match deferrals as far back as 3 months?

If yes, should it from the beginning of the plan year.

I didn't find any language in the amended & restated plan document regarding the possibility that the plan sponsor has discretionary power to back date and match deferrals on X% payroll by payroll.

Thanks!