Technical Blog Post
Why some of the tables showing no stat collected even if auto runstats is turned ON
It's possible some of the tables showing STATS_TIME "-" in syscat.tables catalog table even when the auto-runstats in the database is tunred ON.
The main reason might be, if a table is never accessed, then auto-runstats will not action on that table, even if the table has never had runstats done. This is by-design. This could be applicable for system tables as well as user tables.
Regarding system catalog tables there might be differences of observations from version to version on what table might show the stat not collected. That is based on how the version utilize that catalog table.
Another reason of not showing stat could be due to runstats policy in place to exclude certain tables. But, that is a conscious decision.