Yes, separate generation.
However, I have an update. This issue appears to have "magically" resolved. I made the following changes to each preset in all 12 merged projects (1 parent, 11 children) - and yes, all 12 build presets used to generate the merged output were identical before this. Not sure which of these changes triggered the fix, but it was something:
- General>Use lowercase file names: Removed checkmark; was previously selected.
- Search>Use topic description as search context: Removed checkmark; was previously selected.
- Search>Set search context character limit: Changed from 100 to 150.
- Search>Number of results on a page: Changed from 20 to 10000 (merge consists of over 6.5k topics; audience can use included filters if they want).
- Search>Generate XML sitemap: Removed checkmark.
Was any of those actually causing the issue? Or did changing and saving one of those settings just insert a setting that was missing or corrupt (perhaps introduced at some point while upgrading the projects from 2017 to 2019c to 2019n to 2020)? Who knows? However, the initial search that displayed 1397 characters for one topic now only displays 150** for that topic and the same search - as I would expect.
**It's not a "hard" 150. It seems to vary by a couple characters from one topic to another. Unexpected, but I can live with a single-digit variance.
Note: This also appears to have solved my missing URL/breadcrumbs issue, which is in another post.
Appreciate the feedback from the community.