Impact of Participant/Beneficiary Culpability on Correction?

[BTG]

Our client maintains a DB plan.  A participant was receiving a J&S payment and then died.  The plan sponsor tried reaching out to the (non-spouse) beneficiary for years and never received a response.  Now the beneficiary has died.  Presumably the missed payments are still owed to the beneficiary's estate.  However, is the sponsor required to include an interest adjustment where they made every effort to pay during the beneficiary's lifetime?

[CuseFan]

I think IRS/DOL position would be yes, because the benefit was due and not paid and the plan had the use of the assets.

If the plan had actual contact with the beneficiary, had a valid address, SS#, etc. (which should have been collected and verified up front) then why wasn't the survivor benefit just started? IRS/DOL might raise that question as well.