Thank you, David. My confusion originated from a lack of familiarity with the ANALYZE command. Your responses and Tom’s response have been very enlightening.
The head-scratcher for us is that our statistics became so out of date even though we have the autovacuum daemon enabled in RDS, and according to the docs that does run ANALYZE periodically. Now we know (thanks to your help) to check for this issue immediately when the planner is showing a large disparity between the estimated and actual cost.
Markus E.