Plugin Repository commit doesn’t show up in activity

If your plugin is already in the repository, you don’t need to submit the form to ADD a new plugin, you only need to update the trunk folder to make your update via svn.

Sure WordPress will send you an email to tell you that the name is already use by another plugin and ask you to change its name.

When updating a plugin, WordPress doesn’t care about it, you can make update in the trunk folder and push the older one in the related tags folder that you need to create.

Don’t forget to update the readme.txt to tell WordPress repository which version to serve to users and modify the main plugin file accordling to this value.

i.e : if you want the trunk folder to be be last version, readme.txt must contains stable version: trunk and the main plugin file version: 1.1.
In the tags folder, add a folder 1.0 where the version 1.0 need to be copy.

Hope its helps.