15. All code changes to a plugin that has a Stable Tag of “trunk” must result in the version number being upgraded.
For the trunk and tags method, trunk can be continually updated without version number changes, while tags should generally not be updated past the initial tagging, unless the readme is being updated with regards to supporting the newest version of WordPress.
For more information on tagging, please read our SVN directions on tagging and how the readme.txt works to better understand this. Remember: If you use tags and don’t increment versions, no one will get your updates.