The trustee must recognize that the two pools of money are separate, so they can make the annual ERISA statements each year for each separate pool.
As a side note, I understand that splitting a plan solely to avoid the audit requirement is not looked upon favorably. Is there another reason/division for the split? Some natural division between two groups that are getting different benefits?
The exception only applies only to the Plan that you separate service from after attainment of age 55.
If you roll the funds from that plan to an IRA or another qualified plan they pick up the characteristic of the new vehicle.