dba_sql_plan_baselines.reproduced value not update?

db version: 12.1.0.2.0

rdbms home: /paic/dev/oracle/rdbms/12c/12.1.0.2.170418

we used sql plan management in our production database, recently we found when a plan become unproduced such as index was dropped, the value of dba_sql_plan_baselines.reproduced can't update to 'NO'.

I also tested the scenario in testing environment, for one simple sql, I generated a full table scan plan and a index scan plan in sql plan baseline, after that, I dropped the index, so the index scan plan should not be reproduced, but the value of dba_sql_plan_baselines.reproduced still is 'YES', seems it will never be update to 'NO'. so I want to ask why the value will not update while actually the plan is not reproduced? and when will oracle update the value to 'NO', and how?