Why does the TIMESTAMP# column in the AUD$ table contain NULL values?

According to Oracle Support Note 427296.1:

"In database version 10gR1 and above, the TIMESTAMP# column is obsoleted in favor of the new NTIMESTAMP# column."

So when exchanging the TIMESTAMP# with the NTIMESTAMP# column, my script works as intended, while it had previously showed NULL values:

SELECT DBID "CURRENT DBID" FROM V$DATABASE;

 SET TIMING ON
 SET LINES 200
 COL "Earliest" format a30
 col "Latest" format a30

 PROMPT Counting the DBIDs and the number of audit entries each
 PROMPT Could take a while...
 COL TIMESTAMP# FORMAT A3
 SELECT DBID,COUNT(*),MIN(NTIMESTAMP#) "Earliest", MAX(NTIMESTAMP#) "Latest"
 FROM AUD$
 GROUP BY DBID;

Output:

Counting the DBIDs and the number of audit entries each
 Could take a while...

       DBID   COUNT(*) Earliest                       Latest
 ---------- ---------- ------------------------------ ------------------------------
2367413790       1867 05.06.2014 14.01.30,193254     06.06.2014 06.17.08,485629

The views built upon AUD$, for example DBA_AUDIT_TRAIL and DBA_FGA_AUDIT_TRAIL, will of course reflect the correct columns from AUD$ (NTIMESTAMP#) in their own TIMESTAMP column.