[roger64]

@Divingduck

Thanks for your input but I refered about the toc.ncx file and its navpoints ids.

Calibre use uuid for them and Sigil use incremental values (like 'navpoint-1', 'navpoint-2', etc.). In fact, if you open one EPUB with Sigil and type Ctrl-T, it will rewrite your toc.ncx file and make use of these incremental values.

I was just saying that the incremental values (à la Sigil) seem to be more handy than cumbersome uuid. Both are unique identifiers, at least for the file. I wish I could obtain the same result directly with Calibre.