Practically speaking, what recourse does an employee have who disagrees with the method of ADP cutbacks? Assume the method is incorrect.

How much do you believe you were over-refunded?

If it is a large enoough amount you could consider rocking the boat some. If the test was in fact performed incorrectly, the amount of the over payment to you and possibly others in your company would be categorized as an in-service withdrawal in violation of 401(k)withdrawal restrictions, unless corrected. This could place the entire plan in jeopardy of disqualification by the IRS, if it were discovered uncorrected.

401(k) plan testing can be quite complex, and recent legislation has changed the way that refunds are calculated and allocated amongst the HCEs in the plan.

Tread lightly in this area. You have the right to question the test calculations, but your employer may not be very receptive to questioning. If they are using an outside recordkeeper for the performance of the tests, they probably don't have a thorough understanding of them. They will have to consult with that firm.