Employee Contributions vs. Employer Contributions
In any 401(k), accounts may include both what the employee contributed and what the employer put in. While employee contributions are always 100% vested immediately in a safe-harbor plan, employer contributions may still be subject to a vesting schedule, even in these plans.
That means part of the account (usually employer contributions) might not belong to the employee yet. The QDRO should specify whether the alternate payee (the former spouse) receives only vested amounts as of a defined date, or also a portion of any future vesting, if allowed by the plan rules.

