Sadly it depends.
As Slave and Akira mention, they SHOULD unlock in due course.
Problem being... its rare that the privledge system doesn't crap out at the end of a book. There's numerous books that ended and privledge holds the last X chapters hostage. Wether its the translator/author buggered off or webnovel being so understaffed that they never got around to automating that feature, no one knows.
As suggested, you can leave a reminder in the last available chapter (or see if the book has already had reminders left), if it goes on longer than a month chances are exceptionally higher that the book will land in limbo.