Thank you all for the advice and suggestions. I am investigating the interpretation of how to handle gains and losses to the terminated participants' accounts, following RatherBeGolfing's suggestion. Once I get a response, I will be able to see what to do next.
This is a fine place to work and I am not going anywhere. One incident is not representative of the normal flow of everyday business and there will be a way to resolve this. You can't blame the powers that be for not listening at first. They were relying on a combination of a departed partner's interpretation who had been widely respected as the absolute go to expert on everything, and the document provider's advice. Weigh that against the opinion/misgivings/gut reactions of a new employee, no matter how smart or experienced that employee might be. I am not an ERISA attorney, just an administrator who has been around the block more than a few times.
However, with the citations you have all given, I have more arguing power now, and I will find a solution to this.