Employee and Employer Contributions
Most 401(k) accounts include both employee and employer contributions. While employee deferrals are always considered marital property (if earned during the marriage), employer contributions may be subject to a vesting schedule. If part of the employer match wasn’t vested at the time of separation or divorce, that amount likely isn’t divisible.
Make sure the QDRO specifies whether it applies only to the vested portion of the account. Ask the plan administrator for a current vesting schedule and balance breakdown.

