Failure To Execute a Co-Sponsor Adoption Page

[Guest gaham]

The employer maintains a nonstandardized, prototype 401(k) plan. A separate entity but member of its controlled group began participating in this plan on behalf of its employees at the beginning of this year, but the related company didn't execute a co-sponsor adoption page as is required under the terms of the plan. Can we self-correct by executing the adoption page now with a retroactive date (taking the position that this is a plan amendment to correct the inclusion of ineligible employees) or is our only recourse submitting under VCP? I would appreciate any thoughts.