The title say mass update, you'll ask me : "how much is it a mass update ?"
Well, I think when ALL the pdf files have been updated, you can call it mass update !
All of them have been updated to Arial font, it don't seem anything important said like that, but it change actually a lot of things.
The older files where using what's called a serif-font ; good for printed documents.
Problem : ebooks aren't made to be printed !
So I switched for most recent files to a sans-serif font. Their goal is to be better to read on screens. Yay, that's the whole point of ebooks !
Well, all would have been good in the best of the worlds if there wasn't a BUG !
Using the sans-serif font was making the italic disappear... And when some books abuse of it for distinguishing speech and thought. It make the reading slightly more annoying.
The solution ? Using another sans-serif font ; and I choosed Arial.
In short :
All pdf files have been updated to Arial fonts, making them better to read. I also corrected italics not showing on recent PDF files.