EE 12.2 sys.aud$ not capturing alter user records

Hi, DBAs

This is EE RAC 12.2 on OL 7.4. I'm asked to audit the use of "alter user" commands, so I issued these statements on the database:

AUDIT ALTER USER  BY ACCESS;

AUDIT CREATE USER  BY ACCESS;

AUDIT DROP USER  BY ACCESS;

AUDIT USER  BY ACCESS;

I confirmed that these audit options, by access for success and failure, are in the results from sys.dba_stmt_audit_opts. Parameter audit_trail = 'DB', and unified auditing is FALSE per v$option. I locked a user account to confirm that "alter user" was captured in sys.aud$, but there is no record with action# = 43.