I have sometimes heard collectors talk about setenant issues as tęte–bęche. These are two very different things.
Tęte–Bęche stamps are a pair of stamps where one stamp is printed upside-down in relation to its adjoining copy. The upside-down printing could be intentional or accidental. Some countries, such as France, have created tęte–bęche stamps for many years.
Setenant stamps are two or more stamps with different designs that are joined together. Sometimes the stamps are independent (such as Scott #1421 and #1422) where they do not contribute to an overall design. Sometimes the stamps (such as Scott #1480-83) are combined together for a common design (the Boston Tea Party in this case).
As far as I know, there has only ever been one US stamp that is truly tęte–bęche. The Buffalo Balloon issue, Scott #CL1, is known with tęte–bęche pairs. I know, this stamp was not issued by the USPOD, but it is the closest thing we have to a tęte–bęche issue.
There are plenty of USPS issues that are setenant, but none of them are tęte–bęche in the pure sense of the word. There are a few issues that come close.
Take Scott #3130-31. These are the triangular stamps issued for Pacific 97. There are 16 stamps per pane arranged in four groups of 4 stamps each. It is possible to take two of these stamps and have a back-to-back pair of stamps where one of the stamps is upside down in relation to the other. Some may call this tęte–bęche. I don’t see it that way.