Inherited IRA rules state that while a trust generally cannot be a designated beneficiary, if a given trust is a properly-drafted see-through trust, it can be treated as a designated beneficiary. Correct?

So, under SECURE, if an IRA is left to a see-through trust, and the surviving spouse (an eligible designated beneficiary) is sole beneficiary of that trust, that see-through trust can stretch based on SS’s life expectancy. Is that also correct? (I am uncertain because I believe that sole-bene see-though language in SECURE only appears in the section discussing disabled and chronically ill benes. Does that see-though provision grant lifetime stretch to all EDB’s, or just the disabled/chronically ill?)

Assuming all that is correct – would the stretch option be available to a see-through trust where the SS is only entitled to income off the inherited value, while the deceased spouse’s kids (from a prior marriage) are entitled to the residuary once the SS/step-mom dies? Let us assume for now that the money will be invested in a fixed index annuity where the premium is protected against market loss.

SECURE states that residuary beneficiaries are OK so long as they “do not have any right to the employee’s interest in the plan until the death of all such eligible designated beneficiaries with respect to the trust”. However, in this trust, don’t the kids have a present right (if not present access) to the “basis” (i.e., the amount originally inherited from their dad)? If so, does that kill the lifetime stretch, and force the trust down to out-in-10?