Designating excess deferrals in multiple plans (402g limit)

An individual worked for 2 unrelated employers in 2025 and deferred into separate 401k plans. They deferred $15,000 into Plan A and $15,000 into Plan B. They are not catch-up eligible and they need a 402g refund of $6,500.

Based on what I am seeing in the regs, the individual ultimately determines which plan holds the excess. If you go by the last-in, first-out method - Plan B would issue the refund. But, Plan B has a very generous match and the individual would have to forfeit some of his match if the refund comes from Plan B.

Can the individual choose Plan A as holding the excess? Or, can they designate a portion of the excess from Plan A and a portion from Plan B? For example, can they request $3,000 to be refunded from Plan A and $3,500 refunded from Plan B?

They ought to be able to, but they might need to convince either sponsor the excess has really occurred.  (Otherwise this is a request for a random-ish looking withdrawal absent the knowledge of the other plan.)

Your W2 from each firm should have the amount of deferrals you made while employed by each firm (Box 12).  That should be sufficient proof for all parties.

Yes, and then the person can request however much of their excess from each of the plans as they choose. This is a tax compliance issue for the person, not a qualification compliance issue for either plan.