We’re updating the Checkouts API to allow you to early return a title even after a format has been locked in. This means that the earlyReturn action will always populate after you make a successful checkout.
We’ve updated our documentation on the Checkouts API page to reflect this. The change is currently in the Integration environment. We plan to release this feature on 04-MAR-2019, so please be ready and be sure to update your applications if necessary before then.
Thanks for being an OverDrive API Partner,
-The OverDrive API team