I took the ISSEP exam last month and got a 680

The few questions that I believe sunk me dealt with C&A processes and who uses them. I am hoping that some more seasoned ISSEPs can chime in and set me straight. All of my study materials describe DIACAP as being used by DoD and NIACAP as being used by everyone else. What I cannot seem to find a definitive answer on is who uses the SP800-37 RMF process. What is also confusing to me is the fact that the test is possibly a little outdated with regard to C&A. I know DoD is moving towards updating with something similar to the RMF, but they are not there yet. So should I be taking this test assuming that it is still stuck on the older processes?
My Current Understanding:
DIACAP - used by DoD both agencies and contractors
NIACAP - used by all other agencies, IRS for example
SP800-37/RMF - New Process, not currently required to be used by federal agencies but perhaps being used in the private sector....?
Thank You for any help you can provided. I'm re-taking monday 2/16/15..... Wish me luck!