Yes. Previous research (registered or not) can be incorporated in a registered report in the same way it would be in a traditional paper — as a preliminary study in the main text or pilot study in the appendix. It is important that authors make clear in the text which results were registered and which were not.
How does the review process for registered reports work?
In Stage 1, reviewers evaluate the importance of the research question and quality of the proposed design. At the conclusion of this stage, the editor
