If there is a calendar-year 401(k) plan in which the salary deferral contributions were limited to 15% for 2003, but by mistake amounts in excess of the 15% were deferred, would it be possible to retroactively amend the plan today but effective on Jan. 1, 2003 to increase the salary deferral limit to 75% for 2003?

I can't find anything that would prevent this. 411(d)(6) shouldn't apply. I assume there would be an operational failure for 2003, but if the retroactive amendment is made would that still be the case?

Would changing this provision benefit HCE's or NHCE's? If the amendment benefits predominantly HCE's, you may have a problem.

It would only benefit NHCEs.

I guess one basic question is whether there is any restriction on amending a plan retroactively other than 411(d)(6)? I've heard some people say you can amend a plan to the beginning of the current year, but if you can do it to the beginning of the year where is the restriction against doing it even further back? Or alternatively where does it say you CAN go back tot he beginning of the year?