I know that assets in accounts registered "Pay on death to XXXX" or "Transfer on death to XXXX" while not in the probate estate are part of the taxable estate.
I assume that even though those assets are never in the probate estate and go straight to the named beneficiaries they are subject to clawbacks from the named beneficiaries in the event that the assets of the probate estate aren't sufficient to pay the estate tax (because if there was no clawback, it would be a too-easy way to avoid estate tax!)
Is the assumption true? If it is, how is it enforced?