Decedent's Estate

An estate of a deceased person is a taxable entity separate from the decedent. It generally continues to exist until the final distribution of the assets of the estate is made to the heirs and other beneficiaries. The income earned from the property of the estate during the period of administration or settlement must be accounted for and reported by the estate.    [From Form 1041 Instructions]

Under state probate laws, an estate can be closed in some circumstances even if not all funds are distributed.  In other words, it can be final for court reasons, but not for tax reasons.  What it sounds like you are doing, is telling the beneficiaries to pay tax in 2019 on distributions they may not receive until 2022.  If funds are being held back for three years, there must be some concern that they will be used to pay taxes and creditors, rather than beneficiaries.  If the beneficiaries are happy with paying tax on money they may never receive, I suppose that's their decision.  It wouldn't be mine.