[JimmXinu]

Originally Posted by ownedbycats

Aside from attempting to fetch new chapters for all my fics and getting the "chapters not recognized" error on them, is there any way for FFF to detect ePubs that were not downloaded with FFF?

Nothing in FFF comes to mind. You could use plugin Quality Check's Search ePubs feature to search for FanFicFare in OPF manifest to mark the ones that are from FFF. Might need to section off in a VL or separate library to make that convenient.

Originally Posted by ownedbycats

Also, what exactly does "remove new chapter marks from selected book" do?

If you have mark_new_chapters:true, new chapters will be marked on update. That feature removes those marks.

From defaults.ini:

## If true, when updating an epub that already has old chapters, new
## chapters will be marked in the TOC and chapter header by using
## chapter_title_new_pattern and chapter_title_addnew_pattern to set
## the chapter title.
## If set to latestonly, only new chapters downloaded this time will
## be marked (new) and existing chapters will have any (new) marks
## removed.
## mark_new_chapters can be true, false or latestonly
mark_new_chapters:false

## chapter title patterns use python template substitution.  The
## ${number} is the 'chapter' number and ${title} is the chapter
## title, after applying chapter_title_strip_pattern.  ${index04} is
## chapter number padded with leading zeros (mostly for internal use)
## such as 0001.  ${index} == ${number} for backward compatibility.  A
## few site adapters add additional chapter metadata.

## The basic pattern used when not using add_chapter_numbers or
## mark_new_chapters
chapter_title_def_pattern:${title}

## Pattern used with add_chapter_numbers, but not mark_new_chapters
chapter_title_add_pattern:${number}. ${title}

## Pattern used with mark_new_chapters, but not add_chapter_numbers
## (new) is just text and can be changed.
chapter_title_new_pattern:(new) ${title}

## Pattern used with add_chapter_numbers and mark_new_chapters
## (new) is just text and can be changed.
chapter_title_addnew_pattern:${number}. (new) ${title}