As linked to by @littleadv, Treasury Bills aren't reopened.
Federal Registry July 28, 2004, Part IV, Department of the Treasury, Fiscal Service, 31 CFR Part 356
Sale and Issue of Marketable Book-Entry
Treasury Bills, Notes, and Bonds—Plain
Language Uniform Offering Circular; Final
§ 356.5 What types of securities does the
We offer securities under this part
exclusively in book-entry form and as
direct obligations of the United States
issued under Chapter 31 of Title 31 of
the United States Code. The securities
are subject to the terms and conditions
in this part, the regulations governing
book-entry Treasury bills, notes, and
bonds (31 CFR Part 357), and the
auction announcements. When we issue
additional securities with the same
CUSIP number as outstanding
securities, we consider them to be the
same securities as the outstanding
(a) Treasury bills.
(1) Are issued at a discount;
(2) Are redeemed at their par amount
at maturity; and
(3) Have maturities of not more than
So what is going on with the CUSIP?
Checking the Treasury Direct site:
912796X53 as of EOD 2023-03-13 has 3 Bills with the same maturity date:
||Price per $100
As all Bills are issued at discount to par, it may be better to think of the CUSIP as marking the maturity date for all short term Treasury Bill/auction/non-auction obligations which are due on that date.
Logically if you transacted on a $10,000 USD 52-week Bill maturing on 06/15/2023 at the same date/time as the auction for the 13-week Bill maturing on 06/15/2023, the par value of $10,000 USD doesn't change, only the price/discount value would change matching the 13-week Bill auction discount. The seller capturing the increase in price from the original 52-week Bill issue date.