Advanced Certified Pistol is a credential no longer issued, but not revoked from existing trainer accounts.
In the past, it involved a written test, submission of a resume, and proof of additional defensive pistol-oriented training. Then a committee would meet, grade the test, review the package, and vote up or down. Pretty labor and time intensive.
NRA found that after all that work, practically no one was teaching Defensive Pistol and simply elaborating their email signature block, so they killed the program and authorized anyone with Personal Protection Outside the Home to teach it.