That might not be about what the IRS allows because self-correction means the employer doesn’t ask the IRS.
Among the burdens of self-correction (even before SECURE 2.0 § 305) is that it puts responsibility on the employer and, practically, its adviser.
If, after a self-correction, the plan’s tax-qualified treatment is challenged, the burdens of proof and persuasion are on the employer to show that the failure was eligible for self-correction and that the correction was appropriate.
When a professional is asked for advice, whether written or oral, that a failure is eligible for self-correction, the professional evaluates the liability exposures and other risks of that advice.
About the example you set up, ask yourself this rhetorical question:
Could Belgarath, knowing that States’ laws hold a nonlawyer to the same standard of care that would be used by a prudent lawyer (with the same exposures for liability to one’s advisee and third persons), write something to confirm the failure is eligible for self-correction?