Employee vs. Employer Contributions
401(k) plans include both employee contributions and often a portion contributed by the employer. In many cases, employee contributions are always fully vested — meaning the employee owns them outright. But employer contributions may be subject to vesting schedules.
This is critical in divorce. If the participant (your spouse or ex-spouse) hasn’t met the employer’s vesting conditions, then part of the account you thought was marital may be forfeited — reducing your share. A good QDRO will spell out what happens to unvested funds and how adjustments are handled.

