Excluding service prior to adoption of the plan for vetsing

[Tom]

Plan sponsor has had  401(k) plan in which a participant is 100% in profit sharing.  He wants to adopt a DB plan for 2023 and the employee terminated in 2024. Can years of service be prior to DB adoption be excluded for DB vesting?  The plan document says service for vesting must be recognized for a "predecessor" plan.  Does predecessor include K plan or only a prior DB plan?

Thank you

[Bri]

It includes plans terminated in the last five years, not currently active ones.