Transfers of property occur on the date of death officially.
Technically, with a change of ownership, an allocation is made for profits and losses up to the date of death for the decedent, and afterwards, the beneficiary gets a separate K-1 for the period of time she owned the stock.
if there was a desire to have the K-1 go to the estate, the beneficiary would have to disclaim the bequest, yes?
The shares, and everything the deceased owned. go to the estate on the date of death, unless an overriding document, like a life insurance policy, indicates a different payee. The estate then distributes property per the will or any other legal document or per stirpes.
The trustee of the estate distributes the property of the estate.
If a beneficiary of the estate does not want ot, she can disclaim it.
Nonetheless, either the estate or someone else owns the shares.