Oops...you forgot to get your stamp upon return to the USA. Luckily there is a process to mitigate any potential claim from the country your traveled to. It's called a Certificate of Disposition (COD). It is way to confirm that your goods are currently in the USA.
How to complete a Certificate of Disposition (COD)?
You must complete this form here.
Questions? Review these COD instructions here.
After completing the form, you will need to bring BOTH your goods AND the completed form to U.S. Customs to get signed. Find an office near you here: https://www.cbp.gov/border-security/ports-entry
Once Customs has stamped the form, simply follow the shipping instructions on the back of your Carnet (make sure to send BOTH the Carnet AND COD completed form)
If a claim is received from the foreign customs authority, your company will be contacted—especially if the COD does not resolve the matter. If no claim is filed within 13 months after expiration date, the carnet will time-bar closed.