Though that sounds very certain, I stand corrected. Embarrassingly, there is a way to provide for a Page label inside a PDF, and there’s also a label property in the PDFPage class of Apple’s PDFKit framework.
The latter should make it relatively easily possible to add the page label to the annotation summary. Especially, since DT already displays the page label correctly in its preview pane.
@snakenuts: To atone for my previous erroneous comment, I could try to provide a script that fixes the annotations in the way you proposed. But since I do not use annotations at all, I have no sample summary file to work with. Could you provide such a file, preferably as a Markdown document (while it might be possible to modify an RTF file, too, it’s a lot more work)?