Wouldn't it be great if participants watched over their accounts and promptly reported irregularities? Time for the Plan Administrator to review enrollment and election procedures to add a way to document what they think the participant has elected, for everyone's reference 8 years later. When participants are first enrolled, send them a notice of what the plan thinks their deferral election is, and send another notice whenever participants change their election. Let participants know that they should expect to receive from the Plan a confirmation of any election changes they make.
One could even send fresher notices to the participants each year: "Our Plan records show that you are currently electing to defer n%, which is reflected in the deductions on your paycheck "stubs." If you believe that this is incorrect, please promptly notify us in writing. If we do not receive your written notice within 30 days, this deferral rate will be deemed to be correct."
Kind of a PIA, but serves as a CYA, too.