Exclude Vesting Prior to Plan Effective Date

Prior plan is an non-ERISA 403b effective from 2009 and terminated prior to 2015. They only had employee contributions, never any employer contributions.

The new ERISA 403b is effective 1/1/2015. The plan excludes vesting service prior to plan's effective date.

Can the new plan exclude vesting prior to 1/1/2015 even though they had another plan during that time?