Employee vs. Employer Contributions
One of the first things to understand is the distinction between employee contributions (which are always 100% vested immediately) and employer contributions (which may be subject to a vesting schedule).
If the employee spouse (the “participant”) worked for the Unknown sponsor for a limited time, there’s a chance some employer contributions are not fully vested. In a divorce, unvested amounts cannot be awarded to the alternate payee. Your QDRO should reflect this clearly to avoid future disputes or denials from the plan administrator.

