I was thinking “how can Dorico currently handle this better than Sibelius?”
In Sibelius it’s basically separate files for each number with a fudge (floating title/composer, bar number reset halfway down the page) when you need a new number/movement/song on an existing page. The pain is that if material is added or removed you have to do a lot of page number changes.
Dorico DOES still require a workaround, which I think is this: keep everything in one project but split the full score into as many layouts as necessary. If there’s a need for a new flow to start halfway down page 25, for example, then as much before that (say pages 1-24) goes into one layout, all set to start flows on new pages. Then page 25 is a separate layout with flows starting on existing pages. Etc.