The CSSLP CBK for exam preparation purposes is good, but my understanding is that ISC2 official materials (CBKs, study guides) never aimed to cover all exam questions. There were similar discussions in 2018:
https://community.isc2.org/t5/Exam-Preparation/Failed-the-new-CISSP-CAT-exam-on-April-07-2018/td-p/9...
https://community.isc2.org/t5/Exam-Preparation/CISSP-book-enough-for-the-exam/td-p/14276
Let me quote from these threads:
"I called the (ISC)2 customer service and expressed my frustrations. The representative told me that I should not just rely on one source for preparing the test. "You should study other materials out there" the rep said. When I asked what materials should I look for to prepare, the representative did not have a solid answer for it. "
"No single book, or cram course for that matter, can prepare you completely for the CISSP exam. [...] the exam is designed to check breadth of knowledge and experience over many diverse knowledge domains. The exam is not intended to be passable by a newbie with no experience and only one book or course as preparation."
"I used 3 different sources to prepare for the CISSP; the official ISC2 CBK book, the Shon Harris all in one book and a dummies guide. It took 8 days to study and pass the old paper based exam, but then I had worked in InfoSec for 8 years and IT for 17 years when I took the exam, so had probably absorbed some of the information from practical experience already."
These replies are about CISSP, but the situation with CSSLP is similar, I passed the exam this week.
You have to score 700 points out of a maximum of 1000. If there are topics not covered in the study guide or CBK, your experience should help you score at least 700 points, because most unknown topics can be answered by a professional with the required skill (at least 5 years) and common sense.
