@Aurum2836C,
Something else you might need to know about reading on a Kobo is that it stores the TOC details in its database when the epub/kepub is originally imported. It may be the only ereader brand which does this.
If you resend a book by copying on top of the original (rather than deleting the original then resending), problems will happen if the TOC has changed or if the book's internal file structure has changed between the old and new versions. Sigil automatically enforces its own specific file structure when you open an epub, so you may not even be aware that the file structure has changed.
If your epub edits are something simple like correcting typos or changing CSS styles then you'll probably get away with a simple copy new on top of old. Unless, of course, the epub/kepub filename has also changed - in which case you'd end up with 2 copies of the same book.
Nothing's ever as straightforward as you hope, is it?
