Employee vs. Employer Contributions
The Acme Engineering & Manufacturing Corporation Incentive Savings Plan likely includes both employee (pre-tax or Roth) and employer contributions. Typically, employee contributions are 100% vested immediately, whereas employer contributions may be subject to a vesting schedule. This means unvested employer contributions at the time of divorce may not be available for division.
Your QDRO should specifically identify all vested balances and clarify how unvested portions will be handled (e.g., whether the alternate payee receives any post-divorce vesting). Failing to address this leads to confusion or rejection by the plan administrator.

