1. Employee vs. Employer Contributions
A 401(k) account will likely include employee contributions (fully owned by the participant) and employer contributions (which may be partially unvested). In divorce, only the vested portion of employer contributions is divisible unless the plan allows other arrangements.
The Seattle Tennis Club 401(k) Plan may include matching or profit-sharing funds from the employer. Your QDRO should clearly state whether it covers only vested balances or includes language addressing potential vesting post-separation (if the participant continues to work at the club).

