docker-pkg would not build an image (name:tag) which is existing in the local containers storage or in the remote registry. It considers they already have been build and skip them, so you can consider them immutable once they got built. If an image is not present in the local containers storage, it would fetch them from the remote registry instead of building them. The reason, is that you don't want to have different images carrying the same name:tag!

You can use --snapshot (possibly with --use-cache to reuse local layers and speed it up)

Assuming the image has NOT been published (else docker-pkg would pull it), you can delete it from your local storage and start a build: docker rmi whateverimage && docker-pkg build --select '*whateverimage:*'

Improving the output when every slelected images are up to date is probably worth filing another task :)