If you allow your legacy extensions be auto-upgraded, the system will do its best to detect and avoid creating duplicate extensions. We recommend that you check all your extensions after the upgrade is finished to ensure they’re configured as you’d like.

Resources
To learn more about managing upgraded extensions with the AdWords API, make sure to consult the Feed Services guide. For a code example on how to upgrade extensions on your own, look in the migration folder in all client libraries.

If you have questions or need help with the upgrade, please visit us on the developer forum or the G+ page.

 - , AdWords API Team