Vesting Schedules and Employer Contributions
Most 401(k) plans involve both employee contributions (which are always 100% vested) and employer contributions (which may be subject to a vesting schedule). If your spouse is not fully vested in contributions from the Unknown sponsor, you may not be entitled to the full employer-match portion.
The timing of the divorce matters. If the participant becomes fully vested after the separation date but before the QDRO is filed, courts or the plan administrator will look closely at whether the alternate payee should receive a share of those contributions.

