In my field, it's a common practice to publish a work at a conference first, then extend it (typically with 25%-40% more content) and submit it for publication in a journal.
Often the extension is driven by a subset of the original authors, for example, because the remaining authors lost interest or don't have time to develop the extension. In this situation, the question arises whether it's mandatory to include the non-contributing authors as authors of the extension.
Arguably, the authors have already received the credit for their contribution with authorship of the original paper. On the other hand, their contribution to the original work is still a contribution of the extended work.
Is there any official guideline of how such cases should be handled?