austin3515, you’re right that dividing plans to evade an ERISA § 103 audit would fit only if all plan, trust, investment, service, and related records logically follow the separateness of the plans.
If a collective trust, master trust, or other trust for more than one plan is used, one would want the separateness of the participating plans, and the separate accounting between or among them, to be carefully documented.
Further, service agreements with a recordkeeper, a third-party administrator, and other service providers would show separateness of the plans (and each plan’s trusts), and might incur multiple per-plan fees.
C.B. Zeller, you’re right to describe one of the many ways two or more plans might together use a trust (or a trust substitute, such as a custodial account or an annuity contract). What matters is whether the documents and accounting show the separateness of the user plans.