Employee vs. Employer Contributions
401(k) accounts usually contain both employee deferrals and employer contributions (like matching or profit-sharing). These can be treated differently in divorce depending on whether they are vested.
If the participant is not fully vested in employer contributions, the alternate payee may only be entitled to a reduced portion. For example, if the plan follows a six-year graded vesting schedule, only 60% of the employer match might be available to divide depending on the years of service.

