That's only if all the plan assets are with that carrier, or in other daily valued accounts. We have several plans that have their 401(k)/match funds in daily valued accounts, but the profit sharing account is in a pooled environment.
I am unaware of any published court decision that is on point for your question. Skillful lawyers could argue a wide range of possible interpretations.
If your client is the employer and it prefers a non-plan, it might want its lawyer’s advice about:
how strongly or weakly evidence beyond the document shows that the document’s provision was not the employer’s intent and is not employees’ reasonable expectation;
whether the document may be equitably reformed to get rid of the scrivener’s error and state only provisions the employer intended.
If the plan document is silent on the issue it sounds like an administrative procedure policy that should be documented and implemented on a consistent basis.