Very strange merger situation...

[Belgarath]

Deleted post - information originally provided to me is incorrect.

[MoJo]

So, I still have questions.  Has the C plan already been acquired?  What are it's provisions concerning eligible employees, eligibility requirements and the like?  Proper planning would included that the C plan covers only those who the employer wants included (and often we see this situation where - after the fact - the acquired plan covers "all employees of the employer" which now includes all of A's existing employees, and or those participating in B's plan.  Employees may actually be eligible to participate in multiple plans, and not including them is an operational failure.

I'm not the expert on testing issues, but once you figure out who is eligible for which plan, who is participating in which plan, and how the transition rule may apply (often the plan docs don't specify the transition rule applies), the testing is straightforward - albeit messy....