When Cookie Saver is implemented on your website, it may look like cookies like the Facebook cookies (_fbp, _fbc) does not get extended correctly and still expires after 1-7 days.
However, this is intentional.
As we dont want to impose unnecessary load on the client by extending cookies every time their expiration is updated, we instead keep a backup of the cookie values. Cookie Saver back cookies uses the prefix "_acs" and are always lasting 2 years.
In the case that Facebook updated its own cookies (now capped to 1-7 days expiration) just before the user leaves the website, Cookies Saver will not have extended the updated cookies to e.g. 90 days expiration. However, as the cookies are kept in the backup cookie, Cookie Saver ensures that the Facebook cookies are re-created after the 1-7 days expiration if they were deleted due to ITP.
This is all thanks to the Cookie Saver Preload Script.