When your skill is published you will have a live version and development version. Both the live version and the development version are shown on the developer console.
Any change in the developer portal requires your skill to go through certification process.
When you submit your new version for certification, both versions remain in your list until the new version is certified. Once the new version is certified, it becomes live and replaces the previous live version. All the existing users will have the live/latest version of your skill. A new development version is then created so that you can continue making updates.
Test Your Live Alexa Skills to Maintain a Consistent Customer Experience Over Time