Missed Deferral Opportunity - Match contribution vesting

A 401k plan is going through the correction program to make amends for not giving quite a few individuals the opportunity to make 401k contributions.  When calculating the associated match on the MDO, is it required that the match be 100% vested even if the plan uses a 6 year graded match vesting schedule?

Thank you

MDO and associated match are deposited as QNEC and always 100% vested.

there was another discussion on this about a year ago and the match can be made so that it is subject to a vesting schedule.