There are many sources of the existing USCG exam questions. Lapware, Murphy books, Upgrade U, Hawespipe, Seasources, Google, all of the prep schools, etc. New Undisclosed questions are being slowly added and old published questions are being slowly withdrawn. Most of the exams draw from the same pool of questions. Some exams draw on easier questions from the pool.
The specialized limited license exams that combine multiple topics into one module, like Nav/deck/safety, tend to be quite easy. The pass rate on those combined modules must be quite high.