Employee vs. Employer Contributions
A typical 401(k) includes both your own contributions and those from the employer. While all your own contributions are 100% vested immediately, some employer contributions are subject to vesting schedules. That means only certain portions may be eligible for division at the time of divorce.
The QDRO must clearly state whether it applies to just the vested portion of employer contributions or attempts to divide a larger pool. That distinction often becomes an issue if one spouse believes more of the account is subject to division than truly is.

