Now, if we export the book, the urls are not inside of the book in the xml file. Once we upload, the title of the page it became the url of the epage.
Normally is not a problem, but if we need to keep the urls, can it be a problem.
Some times we change the title of the book and we do not change the url, if we have an old link to some old url, it works, afther import from a backup, it will not work again.
To clarify, do you mean front matter/chapter/back matter URLs?
Yes, each page (front matter / chapter / back matter) have a url. Take a look that page. We have a url https://colomet.pressbooks.com/chapter/prueba-2/ and a name prueba of the book. If I import, the url of the book in the new installation will be https://colomet.pressbooks.com/chapter/prueba-of-the-book/. Normally do no matter. If we have links and we recover a backup, all the links to the pages with new names, will not work anymore.