Because the changes in the worth of these securities are caused by accruing interest, not increases in their fundamental value. And, in accordance with IRS rules, interest always ceases to accrue on the date of death.
IRS Regulation § 20.2031-1 (a) 3 reads: “Any property, interest, or estate which is affected by the mere lapse of time is valued as of the decedent’s death.”
T-Bills, E/EE Bonds are bought at a discount and rise during the course of their lifetime to their face value. This increase is steady and predictable, not subject to market fluctuations — in other words, it is driven by the “mere lapse of time.” Therefore, Alternate Date reports will show the same value for these securities as Date of Death reports.